If your tiller sat all winter it will need a little work. Drain all of the old fuel out of the tank, install a new spark plug and install a new air filter. Put new fuel in the tank [if you still have old fuel in your portable gas tank dump it into your car or truck so you start fresh for all of your small gas engines.

Now crank it over and it may start. If it doesn't start you need carbeurator cleaner. But an aerosol can of carb cleaner and put two squirts in the air intake [remove the new air filter and leave it off while you get the engine running]. Pull your cord, turninng the engine over and possibly starting it. If it starts, great. If not, let it sit for half hour while that carb. cleaner dissolves some of the gum built up in your carberator over the winter. Two more squirts of carb cleaner and try to start it again.
Generally it will start by now. If it doesn't start your carbeurator must be really dirty. You will have to remove it, and soak it in carb. cleaner for about three hours to clean it out.