If you suck something, you hold it in your mouth and pull at it with the muscles in your cheeks and tongue, for example in order to get liquid out of it.

If something sucks a liquid, gas, or object in a particular direction, it draws it there with a powerful force.

If you are sucked into a bad situation, you are unable to prevent yourself from becoming involved in it.

If someone says that something sucks, they are indicating that they think it is very bad.