Tim Weigel covers the basics of change tracking in SQL Server:
There aren’t a lot of parameters here. You can set change tracking on or off, you can specify your retention period, and you can specify whether to enable auto-cleanup or not.
For the retention period, you have the choice of DAYS, HOURS, or MINUTES. If you don’t specify retention, SQL Server will configure change tracking with a retention period of 2 days. If you provide a number but don’t specify the interval, SQL Server will default to days. The minimum retention period is 1 minute.
This post specifically covers enabling change tracking at the database level.