>what is a good site to start with i am not good in math and
>want to get better....
>i am 8yrs old and in 3rd grade.... I would post such a question at the k12.ed.math newsgroup:
https://mathforum.org/epigone/k12.ed.math
You must be a clever fellow to get concerned with your math. I wish you all the best. If you ever have a specific math question, you are welcome to post it here.