While many homes have tubs in them, many of us won’t use it in that manner. The option is there, however, and usually filling up a tub is done by blocking the drain with a tub stopper. A very common type of tub stoppers is a plunger attached to a chain inside a channel in your tub. You will see a lever that you use to move that plunger up and down, cutting of the flow of water through the drain. The problem with this design is that it is possible for the plunger to get disconnected from the chain, and that could cause your tub to stop draining altogether.
If this happens to you, you should be able to take care of the problem yourself.
You need to hook onto the plunger with something that can fish it out of the channel. A simple tool that you can use is a wire hanger with a small hook bent on the end.
After you get the plunger out, you will need to reattach the chain. Make sure you test it that it is the right length before you seal everything back up again. It could be the chain needs adjusting for it to work properly.