1. Yes you can claim your son. For full time students, the months away at college are treated as temporary absences by the IRS. In TurboTax, you will need to indicate that he lived with you all 12 months.
- They are related to you.
- They aren't claimed as a dependent by someone else.
- They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
- They aren’t filing a joint return with their spouse.
- They are under the age of 19 (or 24 for full-time students).
- No age limit for permanently and totally disabled children.
- They live with you for more than half the year (exceptions apply).
- They didn't provide more than half of their own support for the year.
2. If your claiming your student on your return, the 1098-T for educational expenses and the credits that go along with it belong on your return. If he is required to file a return, he needs to indicate that someone else will claim him. You didn't indicate what kind of income the $1400 is. See Does my dependent need to file his own taxes? to determine if he needs to file his own return.
3. Enter the 1098-T form under the Education section of your return under Deductions & Credits. You will answer the qualifying questions and enter any other expenses you had for books, supplies etc. TurboTax will calculate the credit for you assuming you qualify. See Who is eligile to take the American Opportunity Tax Credit?