Grommets and Valve Cover

[Green7mgte]

just a quick question. What are the grommets used for while replacing your valve cover.. I noticed some sets offer them and some don't. You can tell I never replaced mine before or I wouldn't be asking what is probably a painfully obvious question once I get a physical look at them.
also when replacing should I use some sort of "spray" or "sealer?" thanks guys.

im thinking to fit around the bolts on the grommets. but like i said. never physically seen them. any steps or a walkthrough you can point me to would be helpfull.