If I finish a 1Y course in the USA that offers 1 year OPT extension. After OPT extension is finished I have to vacate the USA or if I have found the job and the company that I am working with can help me get an H1B visa or that is not a possible route?
Under the "cap gap" rules, if your company files the H1b petition (which can only be done starting April 1 for an H1b from the next fiscal year) during your OPT, your F1 status and OPT work authorization will be automatically extended to September 30.
If you successfully complete your OPT (and didn't violate the rules for unemployment days, etc.), you remain in status for 60 days past the end of your OPT. If your company files the H1b petition within this 60-day grace period, your F1 status will be automatically extended to September 30, but you cannot work during this time since your OPT has already ended.
Otherwise you would have to leave the US and get an H1b visa if and when your H1b petition is approved.