Here are the corrections for each sentence:

1. Nam is my classmate. He watches TV every night. **(Correct "classmates" to "classmate")**

2. I think collecting stamps is interesting. **(Change "are" to "is")**

3. My dad cooks very well. He loves preparing meals for our family. **(Change "good" to "well")**

4. I enjoy riding my bike to school. **(Change "to ride" to "riding")**

5. We usually go to a small lake out of the city at weekends. **(Change "in" to "to")**

If you need further assistance, feel free to ask!