The grammar is fine. Never describe yourself as "intelligent". It sounds vain. Instead, say "capable". "Volunteer activity" is too broad a concept. It could mean absolutely anything. Feeding the poor? Chopping down trees? Medical assistant? Add a word or two to specify what sort of volunteer activity you perform.

The statement itself is correct, however, it could be improved by making "volunteer" a present participle so it would be "volunteering". Instead of " activities", you could say "in volunteering community services". I hope this helps. If you'd like to practice speaking, I'd be happy to help you. Feel free to look at my teaching profile and send me a message if you think I can help you."

It makes sense, and is grammatically correct, but it might be more correct to say "in the volunteering community"