If I have the free account does that mean i can only accept 100 submission in one month? what if i get more submissions ?

Yes, that is correct that the Free Plan only allows up to 100 Submissions per month. 

If you go over the submission limit your account will be placed into an "overlimit" status and your forms become disabled until either you upgrade or wait for a monthly reset which happens on the first of the month for free accounts.

You can see our pricing plan differences here on our pricing page -       http://www.jotform.com/pricing 

Also, I would like to point out that we do offer free extra submissions to increase your limits to a little more than doubled for free accounts found here http://www.jotform.com/myaccount/getMore.