Question

what is the relation between a molecule and an atom

Answer 1

This will some it up, and provide some understanding. (hopefully lol)
BTW \[Welcome!\]
Atoms make up molecules. You need at least two atoms to make a molecule. Two oxygen atoms will make one oxygen molecule. Two hydrogen atoms and one oxygen atom will make one molecule of water. Atoms are the smallest component of an element. Molecules are the smallest part of a compound.
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Answer 2

Everything you said was right, until "Molecules are the smallest part of a compound."

Not all molecules are compounds, for example, two oxygen atoms combine to make \(O_2\), which is only made from 1 type of element and thus not a compound.