"I don't like it very much." means that whatever you are talking about it is NOT something that you enjoy
Here are some ways to express emotions from extreme hate to extreme love. This is not a complete list by any means but it will give you an idea.
I find this disgusting. (extreme hate)
I hate this.
I don't like this very much.
This makes me feel uneasy. (mild dislike)
I think it is ok. (mild like)
I think it is not bad. (in British English this can mean a stronger like)
I like this
I like this very much (a lot).
This is fantastic (brilliant, super).
Wow, this is the best ever! (extreme like)
There is a sampling of sentences for you.