If you've been dismissed or suspended from college for poor academic performance, you probably have an opportunity to appeal the decision and explain the reasons for your poor grades. Your best bet is to appeal in person (see these tips). If you need to appeal in writing, check out this sample appeal letter. In it, Emma describes her difficult home situation that led to her dismissal. She also talks about her plans for succeeding in the future.
Once you've read Emma's letter, read the critique to find out what she did well and what could use a little more work.