Grease can be a noun or a verb.
It can be a thick oily substance that is used as a lubricant, like between moving parts of a car. "I put grease on the axle so the wheels would spin more easily."
It can be what is left over after cooking with oil or fat. "Bacon grease is very difficult to remove from countertops or pans."
It can be used as in cooking "Grease the pan (this means smear shortening on it), then put balls of cookie dough on the pan."
It is used in expressions more rarely......
"Grease the palm" means to bribe someone.
"Grease the skids" means to help things run more smoothly....