I heard site traffic will help to get listed in top SERP positions. like, if i get x number of hits that would boost up my performace in SERP ranks. How far it's true..?
its not that how much traffic will get you up in SERPs. However things like CTR matter. If a user searches for "xxx" keyword and your site ranking 3rd. He didnt like the 1st and 2nd search result and instead click yours. That means your site is perhaps more suitable for the keyword. If this happens more often, your page would move to 2nd results and so on. hope that helps.
If that traffic will then backlink to your website, I would assume that your SERPs will rise. However, if your website is exceedingly popular in your community, yet not listed in Google - there is simply no benefit to your SERPs. In effect, if your visitors link to your website with the desired anchor text, your SERPs will definitely raise in rankings.
you just heard a very wrong info...traffic has nothing to do with ranking in SERP but a good ranking in SERP will increase a chance of driving a traffic. also, hits is a useless stat of a site, so just do not mind it at all...