Rule 9.1 states that a draw should be offered after you have moved and before you press your clock. A draw offered at any other time is still valid, but it may be considered as distracting or annoying your opponent if you offer it whilst he is thinking. Repeated draws can be punished in a tournament if the arbiter agrees that the draw offers are excessive. The arbiter could award extra minutes in such a case.
When you offer a draw, or when your opponent offers you a draw, this should be noted on the scoresheet by adding a '=' after the move when it was offered.
A draw can be accepted by shaking hands with your opponent, or agreeing verbally. A draw can be rejected verbally ("no thank you"), or by touching a piece with the intention of moving it or capturing it.
It is important to remember that the claim of a draw under 9.2 (three times repetition), 9.3 (50-move rule) or 10.2 ("2-minute rule"), is also equivalent to an offer of a draw. The opponent can accept immediately if he so wishes.