Check the air filter is not choked solid, and/or choke valve is not stuck closed. if not, proceed ......
Assuming the fuel is fresh, and it's fuel (as opposed to water) on the pug, you have an ignition problem.
Try a new plug first. If no luck, check for a chafed/shorted kill wire. After that, (and assuming a machine less than 20 years old), the coil is suspect.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix lawn mowers.