Super smart! As we discussed, atoms are like letters. Just the way you can take different combinations of letter and form different words, different combinations of atoms will lead to different substances.
For example, there are millions of different substances (compounds) that are formed just from different combinations of Carbon (C), Hydrogen (H) and Oxygen (O) atoms. In a substance, you may have 1 Carbon atom, 2 Carbon atoms, 1000 Carbon atoms, etc. Same with Hydrogen and Oxygen. Each different combination of these atoms is a unique substance.

As you can see in the image here, with 5 letters, we can form several words. Similarly, with H, C and O, we can form several compounds (only a few are shown here).