PicGif and PicGif Lite can be installed from the Mac App store. To open the App Store, type:
This will open Spotlight, and then you can search for:
cmd + space bar
Once you've opened the App Store app, you can search for "PicGif" and install the app.
From this preview screen you can select a few important options. One of the most important options is the frame count. This determines how many frames this video will be divided into. You should take into consideration the desired length of your gif. I typically leave mine at 24 frames.
The size (dimensions) of the gif is one of the biggest factors that determine how large the file size will be. You generally want to keep the file small especially if you're using this gif on the web. A good size for a gif is the default 360 x 240, you can make it whichever size you want.