These sentences have two subjects and two main verbs:
These sentences use and, but, or.
Subject + Verb + ...(,) and (Subject) + Verb + ....
Example: Homer's mother went outside, and she was scared. OR
Homer's mother went outside and was scared. *
Example: Quentin helped him, and Homer built his second rocket.
Subject + Verb + ..., but Subject + Verb + ....
Example: The first rocket wasn't successful, but Homer didn't quit.
Subject + Verb + ..., or Subject + Verb + ....
Example: They needed to learn how to weld, or they needed to get help from someone.
*If the subject is the same in both clauses, you do not need to repeat it. Also, do not use a comma.