30 wt
Any straight 30 weight should do.
5w30
Your owner's manual should explain that.
Sae 30w
10W30 can be used, but SAE30 is best. 10W30 can run a bit hot, in warmer climates.
SAE 10w30 full synthetic any major brand.
what grade of oil on this engine
Depending on the model of the Craftsman lawnmower, there is either an oil plug underneath the deck of the mower which needs removed to drain the oil or the lawnmower needs tipped on it's side to allow the oil to drain out through the oil cap area. Once oil has drained you will want to refill the oil until the dipstick registers "full".
30 weight oil can use car oil or lawnmower oil same oil
youtube - push mower oil change.... oil plug under mower deck
If its a push lawn mower. It has no oil release. The mower burns the oil. All you do is replace the oil when it gets low.
If the lawnmower has two compartments one for gas and the other for the oil, then put gas in the gas and a 30w type oil in the oil compartment. Simple as that. If you have an engine with only one compartment then you'll need to check on the manufacturers suggestions which is usually 40:1 or something close.