There really are loads of players available, & they tend nowadays towards 3 camps: self contained, Direct Show, & some combo of both with Blu-Ray &/or DVD licensing. Self contained players like VLC are pretty easy to understand -- add audio &/or video & it [hopefully] plays it. The players that use licensed code & features are easy to understand, since their purchase price includes whatever it takes to play retail discs with their usual DRM. Direct Show is harder.
With Direct Show you install files that are more individual tools that any app can use in Windows. They're called Direct Show filters, for any function you can have more than one, they can conflict with software or each other, and it's difficult [if/when possible] to tell an app "use these & not those". Their pretty much sole advantage is that you can often do more, because you're not limited to what one company includes with their app(s). The Zoom Player uses Direct Show -- you get the DS advantage & disadvantages.
Zoom Player also bills itself as a Media Center app. Media Center apps traditionally offer a very simple interface you can navigate with a remote, but that's changing, as we're more used to Smart TVs & such today. It's also becoming easier & more common to handle all that navigation using a smartphone or tablet via WiFi. A traditional media center app also often includes something like a video database, keeping track of your stored videos -- nowadays that capability isn't as called for, what with streaming & keeping videos in a single folder to better work with cells, tablets, media players, smart TVs etc.
If you're inclined to use one or more DS players &/or video related apps, get the Codec Tweak Tool & Win7DSFilterTweaker -- one or both may be extremely handy if/when something breaks.
http://www.videohelp.com/tools/Codec-Tweak-Tool
http://www.videohelp.com/tools/Preferred-Filter-Tweaker
The Zoom Player site & comments on the GOTD download page talk about full-screening video -- the site also talks about aspect ratio. This tends to be a really messy can of worms. In a nutshell, do what you have to, as much as you have to, until things look good to you, & optionally any other viewers.
Basically when movies &/or video is shot, it's just like a photograph -- thin people are thin, fat people fat, squares are square... you get the idea. Stretch video in one direction or the other, & that changes. Stretch video in both directions, height & width, & you're usually OK, though you'll sometimes lose subs. Most of the time if you're stretching video you're using a HDTV or maybe a equivalent PC or laptop screen. In those cases, as possible, let the display hardware do the stretching -- it's faster & better than most software, & besides, most HDTVs come with several modes of stretching built in that minimize distortion.
Why do people stretch video? Because some people are more interested in having the screen filled than they are in having video displayed with the highest quality. It's annoying to some to have a 16:9 regular broadcast or DVD video centered on an HDTV screen, surrounded by black bars on all sides. But it's normally the best picture as-is.
Now, when player software full screens video it may or may not preserve the original aspect ratio. Player software may or may not have switches or controls to change that behavior. DVD & standard TV programming uses non-square pixels, meaning for it to look right the player has to alter the video frame size that's displayed. Players may or may not do that, whether they do or don't compensate can depend on the video format, & players may compensate by altering the frame size whenever they play video that's the same frame size as on DVDs, whether it uses non-square pixels or not.
Anamorphic video adds to the confusion -- anamorphic video is stored in a smaller size frame that's supposed to be stretched when played. With DVDs it's likely because there was no larger frame size when they 1st created DVDs -- otherwise it saves space, since there are less pixels to store. A 16:9 DVD video has no defined expanded frame size -- major apps use different, but very close sizes. Most everything else includes the expanded frame size in the file(s), so *compatible* players expand it correctly on playback. IMHO when a player [like Zoom] has an anamorphic switch, it should be labeled stretch, same as many HDTVs -- if it was capable of understanding the anamorphic video it would expand it itself to the correct size, but it's not so it's just stretching in case you think that looks better.
Using your PC, playing video on a HDTV is very often just like playing it on a 2nd monitor -- you drag the player's display window to the 2nd monitor, just as if it were on your desk, or you use the software controls for an external monitor on your laptop or tablet/cell. Or sometimes you'll stream audio &/or video from your tablet/cell to a media player, which may be built into a Smart HDTV, which handles frame sizing & such. If you're using a tablet/cell or PC/laptop & the player software distorts the aspect ratio, & sometimes if it doesn't, it may show up distorted on the HDTV. Players may size the height or width of a video to fill the screen, maintaining the aspect ratio & leaving the rest blank, which shows up as letter or pillar boxing. Blank is not the same thing as having that letter or pillar boxing in the video itself, so the same video that looks *right* on one display may look very wrong on another.
And if you weren't confused enough already, lots of PC/laptop graphics hardware can recognize when it's connected to a HDTV, & many times it will misread a PC monitor as an HDTV too. When it thinks it's connected to an HDTV, all the display properties, & more, can change. If you use a 1080p PC monitor & play video on a 1080p HDTV that's normally OK -- little to fuss with. If they're different display resolutions, things can be not so nice & neat -- you may even lose a fair amount of visual quality in the bargain. If the HDTV's connected when the PC boots, it can throw off your regular display in favor of the HDTV. Win8/8.1's improved in that regard, but being different also means not all software works right with the way win8/8.1 works.
In summery, if anyone says do this & this & bang, everything will work, **Maybe**. In fact, sad to say, it's not completely, 100% certain if everything seems identical between your setup & theirs. Tons of variables & when you get into this stuff, Windows can have & act on its own whims. Working with win7's Media Center & external hardware, I've set it up & had it behave one way, restored a backup so the starting point was identical, done it again with different results, then gotten different results a third time! All of which goes to why Media Center became a paid-for option in win8 -- the majority of people won't fool with using Windows to put video on anything else.