Final answer:
Commas belong in between independent clauses joined by a coordinating conjunction, before a coordinating conjunction when it connects two independent clauses, and before the coordinating conjunction 'and' in a compound sentence.
Step-by-step explanation:
The comma , is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe or single closing quotation mark (') in many typefaces, but it differs from them in being placed on the baseline of the text.
Commas belong in the following places: Between two independent clauses joined by a coordinating conjunction (e.g. 'and', 'but', 'or'). For example, 'I finally found my keys, and I got to work just in time.' Before a coordinating conjunction when it is used to connect two independent clauses. For example, 'Mrs. Contreras threw out her old coffee table and cleaned the carpet.'
Before the coordinating conjunction 'and' in a compound sentence that contains more than two items. For example, 'I let my neighbor borrow my phone, because she said hers was tapped by the police.'