1. Click onto "Trust settings" link. You will have a list where you can add users you trust, or distrust (for distrust you put a ~ in front of user name). Don't forget to click Update
2. If you have a valid opinion on somebody, you can add your trust feedback to another user. If you consider it trustworthy, make it positive, if untrustworthy make it negative, or if you want to just inform for caution, you can make it neutral.