When you join two or more main clauses in a single sentence, the result is a compound sentence. Compound sentences are good for presenting two or more related ideas and giving them equal emphasis:

For a closer look, click on each image to enlarge it.

Be sure to put a comma between the main clauses of a compound sentence, and use a coordinating conjunction between them, or between the last two of them:

I love both activities, but I need to give one of them up.

I could quit the band, or I could quit the radio station.

I don’t have enough time to study, I never see my old friends, and I’m not even making money.

These are the coordinating conjunctions:

and  but  or  nor  or  so  yet

A compound sentence without any conjunctions or commas is an incorrect, hard-to-follow run-on:

I don’t have enough time to study I never see my old friends I’m not even making money.

A compound sentence with commas but without a conjunction is an incorrect comma splice:

I don’t have enough time to study, I never see my old friends, I’m not even making money.

If you don’t want to include a conjunction in a compound sentence you’ve written, a correct option is to put semicolons between the clauses:

I don’t have enough time to study; I never see my old friends; I’m not even making money.