To use the camera tracker select a video in your timeline and click it twice to open the footage in the Footage Panel. Now set and in and out point for your footage. Next, select the footage you just trimmed in the footage panel and then either right click or use the File menu to Create New Comp From Selected.
Inside that comp select the footage, change the work area to Motion Tracking, then Track Camera. Everything should work fine if your shot is a shot that can successfully be analyzed. Not all shots can.
If your AE is crashing when you try to track motion then you probably are not running the latest version of AE. Make sure your apps are up to date buy checking the Creative Cloud App for updates. There was a bug in and earlier version that caused a crash when motion tracking was used.