Mac-Based Editing Tools
Many Macs come with iMovie installed. If not, you may have to pay for the software. There are many guides and tutorials online, but this is a great starter from Make Internet TV.
To import files into iMovie from your computer:
1. Open iMovie, Create New Project
Open iMovie and create a new project using File > New (Apple + N).

Name the project, choose a destination and then press Create.
2. Import the Videos
Use File > Import (Apple + Shift + I), and browse to the directory containing the videos. Select all the video files you plan to use and click open.

If you cannot use or find the videos, they probably aren’t in a Mac compatible format (the files might end in .avi or .wmv). You can try converting them to the .mp4 format with the free video transcoding software ffmpegX
3. Videos Appear in the Clip Library
If all went well, your footage should appear in the clips library. Just click on the name of a clip to rename it.

To edit film with iMovie:
For starters, look at this introductory tutorial video. More videos and tips can be found at Make Internet TV.
To export and make your film web-ready:
1. Export (with expert settings)
Use File > Export (Shift + Apple + E) to bring up the export dialog. Select the QuickTime icon, from the top menu.

Make sure you set it to Compress movie for: Expert Settings.

Now press Share.
2. Save exported file as…
Once you press Share, the “Save As” dialogue will pop up.

Now set Export to Movie to MPEG-4 and then click Options.

Much like digital photography, once a photo is compressed and the original file is destroyed, it is impossible to reclaim lost resolution and clarity. You can archive an original, but watch out — video can eat copious amounts of drive space. For details, see Archiving for Mac.
3. Pick Your Settings
Once you press Options, a new window will pop up. Set the File Format to: MP4.

Highlight the Video tab, and use these following settings:

Next, highlight the Audio tab, and use these settings:

Finally, highlight the Streaming tab, and use these settings:

Now just press OK…

And then press Save.

The amount of time it takes to compress video depends on the speed of your computer, the length of your video, and your settings.

Export Settings Explained (click the link and scroll all the way down.)
Once you figure out what some of the jargon means, you can easily adjust the size and quality of your videos.
What’s Next? Start Editing