Monday Mechanics:(In)dependent clauses

Strunk & White say: Put a comma before a conjunction that introduces an independent clause.

Okay, what does that mean?

Conjunctions are: and, but, or, so, yet…

What they're saying is when you have a sentence and you're joining it with a phrase that can stand on its own (independent clause, in italics), you put in a comma:

The bridge was rickety, so I had to tightly hang on to the rope.

"So I had…" could be a sentence by itself but for artistic reasons, I want it to be with "the bridge...