"What DOES stick mean? Because I often see this word being used in many (different) ways."
Stick as a noun can be a long thin piece of wood/part of a tree. Or anything else that's long and thin. A lollipop comes on a stick.
Stick as a verb refers to things holding together. You use glue to stick things together. Or anything else that is stickY. If you spill a drink your foot might stick to the floor.
You can also stick something somewhere. It means you put it there but usually not very nicely. "The dentist stuck his finger in my mouth without any warning."
You can stick your tongue out.
There are many phrasal verbs with stick - stick around, stick with etc.