Let the engine warm up then you pour in 1/3 of the can, let the engine suck it in. Easiest to pour the 2/3 into the gas tank, then suck up the remaining third. After the seafoam is sucked up shut the engine off. Best to get a second person to shut it down and give it gas while sucking it up to keep it from dying.
Don't forget the fuel filter, it can cause problems too.