The Scroll of Esther (Megillat Esther) is read both Purim night and by day. It's best to hear it in the synagogue, because being part of a larger group gives greater publicity to the miracle. It should be read from a kosher scroll and every word must be heard.
The custom is to turn a gragger (noise maker) at the sound of Haman's name, which follows the command to erase the remembrance of Amalek (Deut. 25:17-19).
(Adapted from aish.com)