The word 'stuff' is another way of saying things or belongings. Example: I have a lot of stuff in my house It will be hard to get rid of of all my stuff when I move to a smaller house Do you want to put your stuff in the hotel room? Women carry a lot of stuff in their handbags. 'Stuff' can also mean liquid Example: Can you put this sun lotion stuff on my back? When I have a cold this stuff comes out of my nose. 'Stuff' can also be used as an expression of dismay Example: Stuff you! I am not going to do your work for you. You can get stuffed!

Both Jura's and Mike's answers are good. I might add that "stuff" is informal. If you were talking to a somebody you just met in a professional situation, you would use "things" or refer to the object(s) directly. "Hello Mr. Smith. Where would you like your things put?" The people at a hotel would tell you "We will bring your luggage to the room." If you are with friends, "stuff" is perfectly acceptable.

I forgot to bring my stuff. What kind of stuff are you looking for? I need to get some batteries 'n stuff. He's the right stuff. This vest is made out of the same stuff marines wear. Etc.