Step 7 of 18 of the SMILES tutorial. Every bond can be written in full, and most never are. C-C-O is ethanol with each single bond spelled out, and c1:c:c:c:c:c:1 is the benzene of the previous step with each aromatic bond spelled out — both mean exactly what CCO and c1ccccc1 mean. The symbol is dropped because two adjacent atoms are already bonded: single by default, aromatic when both atoms are lowercase. That is why - earns its keep in one place — c1ccccc1-c2ccccc2 is biphenyl, where the bond joining the two rings would otherwise be read as aromatic, and the second ring takes a fresh ring bond number. The one symbol you can never leave out is the opposite of a bond: a dot says the two atoms are not bonded at all, which a later step uses to write salts.
It opens on c1ccccc1-c2ccccc2, 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.