To grip something is to hold it firmly. You might grip the TV remote to keep your roommate from trying to change the channel.
When you want to hold on to something, you grip it. If your hands are strong and you can hold things well, you have a good grip. Grip is also the roughness or texture of something. A steering wheel has good grip if your hands don't slip while driving. This word can be also be used figuratively. If you’re upset, your friend might tell you to “get a grip” — that is, get a hold of yourself.