What is a conjunction?

What, you've never seen Schoolhouse Rock?

Coordinating conjunctions: AND, BUT, OR, for, nor, so, and yet.
(The first three are the most commonly used.)

What do coordinating conjunctions do?

They join words, phrases, or sentence parts.

What does this have to do with commas?

When you combine sentences with a conjunction, you must put a comma before the conjunction.

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