Step 2 of 18 of the SMILES tutorial. Write atoms one after another and SMILES joins each to the previous one with a single bond. CCO is a three-atom chain — carbon, carbon, oxygen — which is ethanol. Nothing in the string says how many hydrogens each atom carries: the parser fills them in from the valence of the element as implicit hydrogens. Direction is irrelevant, so OCC is exactly the same molecule written backwards — try it.
It opens on CCO, which you can edit in place: the structure follows every keystroke, and so does the notation when you draw instead.
Convert between chemical structures and SMILES in both directions, search a list of structures by substructure or SMARTS, and learn the notation step by step. Everything runs in your browser — no structure you open ever leaves your machine — so the tool needs JavaScript.