There are several reasons why your mower will not start. There could be an obstruction in the blade, a petrol mower could be low on petrol or the fuse could have blown in an electric mower.
starving for fuel
dirty carb bowl or water in the carb
It depends on if you bought a pull start mower or a power mower. The pull start mower will have a handle you have to pull hard to start it. The power mower should have a button that simply turns it on. Make sure there is gas in the pull start mower.
Blocked air filter, need spark plug replacement,
did you check and make sure you have plenty of oil. or maybe your lawn mower just needs a break.
make sure the gas valve is turned on and you put the air filter in right
your electric motor(I assume) probably wont have enough torque, That is on a Riding type mower, not a push mower, it might work on a push mower as long as its not self prepelled, because your motor probably still wont have enough torque!
bad bearing
replace it
replace battery & starter solenoid.. possibly carb.
get a new one
because it needs a 1600 vee dub engine in it to make it go faster to have lawn mower races