1. Used at the end of all sentences which are not questions or exclamations. The next word should normally begin with a capital letter.

2. Used after abbreviations. If a point making an abbreviation comes at the end of a sentence, it also serves as the closing full stop, e.g.

She also kept dogs, cats, birds, etc.
but
She also kept pets (dogs, cats, birds, etc.).

3. When a sentence concludes with a quotation which itself ends with a full stop, question mark, or exclamation mark, no further full stop is needed, e.g.

He cried 'Be off!' But the child would not move.

But if the quotation is a short statement, and the introducing sentence has much greater weight, the full stop is put outside the quotation marks, e.g.

Over the entrance to the temple at Delphi were written the words 'Know thyself'.