There are lots of great linear video-editing apps on the market today. Final Cut Pro is one of those apps, and it's a great one to use! The problem is two-fold for most who are looking for a simply editing app... 1) it can be expensive (it's all relative, I know) and 2) it can be complex (again, it's relative).
OS X has a simple video-editing app built-right into the system. In fact, it's probably an app that you use all the time, and likely didn't know that it can be used for simple editing.
The default app to view video files on the Mac is QuickTime. Unless you looked for it (and why would you?), you may not have noticed that you can also perform simple video edits in the same app. No, you won't be able to add transitions and green screen effects like you can in "real" video-editing apps, but if you're looking for something to just trim a video... this is the tool for you!
To trim a video, we first need to open the video in QuickTime. Once the video is open, we go to Edit > Trim...
At this point, you will see a timeline of the video at the bottom of the screen.
To trim the video, simply drag each end of that timeline to where you want to cut the video, then click "Trim". That's it! You can now save the new video and use it however you would like.
This is great for shortening videos to use in a Keynote slide deck, email to a friend, etc. This isn't the only way you can use QuickTime to edit video. Now, it's up to you to explore some of the other options that are available!