It maters what type it is but is properly the fuel line
Try spraying start gas into the air cleaner.
It means the engine has been fed too much gas. If you depress the gas pedal on a car or truck many times before you start it, the same thing will happen. A gas engine, whether it is a small lawn mower engine or a truck's engine works the same. It needs a certain ratio of gas and air in order to create the explosion in the piston chamber that makes the engine work.
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.
I am assuming that the mower doesn't start.... My first guess would be that you are not getting spark to ignite the gas in the engine. Check to see if you have spark at the spark plug.
it needs gas
Most mowers unless electric have a lever that works as a throttle/choke to start your mower. If you just pull back on the lever till the throttle/choke no longer allows gas to the engine this usually shuts it off.
Check your fire and gas.
The symptoms of a bad lawn mower battery include difficulty starting the mower, slow cranking when trying to start the engine, and the need to jump-start the mower frequently.
If all oil the mower will not start. If only a little oil, the mower may start but run rough and smoke very much.
Wish it to start.... or if you ran out of wishes... check the gas.....
It won't run on pure deisel.
There should be a sticker/stamp an the engine somewhere. It will give you a few specifications about the mower.