Step 14 of 18 of the SMILES tutorial. A dot separates two components that are not bonded to each other. C[N+](C)(C)C.[Cl-] is tetramethylammonium chloride: a cation and a chloride in a single string, one salt. Order does not matter and you may use as many dots as you need, so CC(=O)[O-].[Na+] is sodium acetate. A zwitterion is the opposite case — in [NH3+]CC(=O)[O-] both charges sit in one connected fragment, so there is no dot.
It opens on C[N+](C)(C)C.[Cl-], 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.