Commas: The second set of rules…
1. Use commas to set off introductory elements at the beginning of sentences.
EX: If they want to win, athletes must practice daily.
EX: Wanting to win, athletes practice daily.
2. Use commas to set off appositives and other nonessential (extra) information.
EX: My house, a traditional colonial, needs some remodeling.
EX: The managers, who sought higher profits, hired temporary workers to replace full-time staff.
EX: Bob Jones, checking tickets at the counter, asked for a form of identification.
3. Do NOT use a comma to set off essential information that is needed to understand the meaning of the sentence.
EX: Managers who are seeking higher profits must hire temporary workers to replace full-time staff.
EX: The person checking tickets at the counter asked for a form of identification.
Go here to practice: