What does sucks to suck mean?

To sharply inhale. To suck is to draw a fluid (liquid or gas/smoke), usually into the mouth (or into any container in which air pressure can be varied) by reducing air pressure; the variant suckle is used when this is done by babies who are sucking milk from their mother's breast.

In modern slang, this is often used as an insult, based on the connection to oral sex.