Johnny and Bill threw the baseball together.

Notice that the guys are two subjects, therefore they constitute a compound subject: JOHNNY, BILL.

Ex of a compound predicate.

(Same principle. There will be two or more verbs.)

Johnny hit the ball, ran to first, and slid into third.

(Here you have three verbs making the compound predicate: HIT…RAN…SLID

The following example is NOT an example of a compound verb:

He HAS BEEN sick.

The two words HAS BEEN are a part of the same tense, the present perfect. Together they do NOT constitute a compound verb.

He HAS BEEN SICK but IS GETTING better.

That IS a compound predicate. Caps are verbs.