Here are the sentences with errors and the corrections:

1. She donates clothes for homeless people twice every year. (Correct)
2. Many people don't know what to take part in community service. (Correct)
3. They do volunteer work, so they like doing something useful. (Correct)
4. We have raised money for people in need since 2020. (Corrected: "for 2020" to "since 2020" to indicate a continuous action)
5. Students can make and sell sweets to raise money for local children. (Correct)
6. We all should take part in community service because it helps us to develop ourselves. (Correct)
7. I want to be a volunteer but I don't have time. (Corrected: "didn't have" to "don't have" to match the present tense)
8. We took a lot of photos when we visited an orphanage last month. (Correct)
9. Students grow vegetables and give them to a nursing home. (Corrected: "for" to "to")
10. We have a lot of fun and learn many things from these activities. (Corrected: "the activities" to "these activities" for clarity)

1. for → to
2. what → how
3. so → because
4. for → since
5. (no mistake)
6. to develop → develop
7. didn’t → don't
8. (no mistake)
9. for → to
10. (no mistake)