[Quiet Man Cometh]

Honestly, I'm not sure. Grammar is not my strong point. I passed it all by instinct and feel. After looking it up, a "clause" appears to be a single thing a sentence is about.

I break things down into basic language when I can. I find it helps with understanding. At its most basic, a sentence should have two parts: a thing (subject), and something about that thing (predicate).

"I (the thing) have a dog (something about the thing)."

"He (the thing) pooped (something about the thing)."

At its most basic, that makes up a complete sentence.

Each of those sentences has one clause.

"I have a dog." = one clause.
"He tried to eat me." = also one clause.
"I have a dog and he tried to eat me." = two clauses, separated by "and."

According to that poster, you can use a semi-colon in place of that "and" to separate those two clauses:

"I have a dog; he tried to eat me."

This is how I teach myself these things. It's sort of the extreme of "back to basics."