A plug is something that is inserted into an electrical outlet and delivers electricity to a machine. You can also use this word when inserting something that is not electrical. This man, for example, is plugging his fingers into his ears:
Why is he doing that?
These sentences show how to use "plug" as a verb:
Denise plugged in her TV and turned it on.
You need to plug this air conditioner into a special outlet.
Bill unplugged his laptop before leaving the coffee shop. (unplug = take the plug out)
Plug up the sink before you put water into it.
If you plug these numbers into the formula, you should get an answer to your question.
The toilet is all plugged up. Get a plunger.
Today’s guest on The Tonight Show is going to plug his latest movie. (plug = promote for commercial gain)
These sentences show how to use "plug" as a noun:
Take the plug out of the wall before you do any work on an electrical appliance.
Most plugs nowadays have three prongs instead of two.
Henrietta is on life support, but her family wants the doctors to pull the plug because she will probably live the rest of her life in a coma. ("Pull the plug" is an expression that can be used when deciding on matters of life and death in a hospital.)