To render a video,
1) Go to the Composition with your final product, (The tab which has the full, final thing)
2) Go to 'Composition' in the standard toolbar at the top.
3) Look for 'Add to render queue,' click it.
4) It will open up a new tab.
5) There you will see the name of you Comp.
6) Play around with the settings there to render it to your likings. (I reccomend Quicktime Movie, it's higher quality

)
Hope this helped, Tell me if it did or if you have any doubts.
~CME