Post Model # from under seat. You need the following for engine to start: check engine oil level on dipstick, add to full if low, fully charged battery, fresh gas in tank, engine compression, check air & fuel filters, good spark. Remove spark plug & inspect for replacement or clean gently removing carbon & check gap at .030 with gauge reinstall & give her a try. If no start you will need to check valves for adjustment, compression release may not be functioning properly. Do not panic, we can walk you through procedure, most important: we need engine information.
Post all information from engine, thanks, Mark