A bathtub is a large container that you get inside to wash yourself. Most people call bathtubs baths, or just tubs.
A club is a very simple weapon, usually made from a piece of wood that is thicker at one end than the other. Clubs are usually associated with very primitive humans.
A club is an organized group of people. Clubs are generally formed around a common interest of all the members, and typically charge some kind of fee for membership or have some other restriction on who can join. You may also be interested in the weapon, club.
A grub is the immature form of many insects, particularly beetles. Grubs usually live in the ground or in fallen leaves, eating rotting vegetation. The grubs you commonly see in your backyard will grow up to be either beetles or moths. Grubs all look quite similar to each other but can look dramatically different to the adult insect they will turn into.
A pub, sometimes called a bar or in some areas a hotel, is a place where alcoholic drinks like beer are sold. Pubs are a place for people to go and have fun with friends, play snooker or darts, listen to live music, and generally have a good time.
You rub something by pressing firmly against it and moving backwards and forwards. People rub metal things with a cloth to clean them. People rub their eyes when they are tired. And dogs love having their tummies rubbed.