I EVER HEARD= In British English we would say "I've ever heard", with a present perfect tense, because we are talking about your life experience. But American English prefers the simple past for past experience.

I JUST MET= (meet - met - met) Again, British English would say "I've met" with a present perfect, while American English uses the simple past. This construction, with JUST, means that the action happened very recently. He will use the constraction again later, when he says "I just kissed a girl".

NAMED MARIA= Called Maria; whose name was Maria.

FOUND= (find - found -found) Found out, discovered.

HOW WONDERFUL A SOUND CAN BE!= For exclamations we use HOW with adjectives (as here) and WHAT with nouns, and we don't make inversion because it is not a question:
- How tall are you?
- How tall you are! (= you are so tall!)
- How big your house is! (= your house is so big!)
- How big is your house? (I'm asking)

LOUD ~ SOFT= To speak loudly is to speak with a strong voice, so everybody can hear. The opposite is to speak softly, as in a whisper. In the song, "loud" and "soft" are adverbs (they describe how you say the word "Maria"), so they should be "loudly" and "softly", but in English (especially in American English) it is very common to use an adjective instead of an adverb of manner:
- I'm feeling good = I'm feeling well
- Love me tender = Love me tenderly
- Go there quick! = Go there quickly!

STOP SAYING= The verb STOP may be followed by infinitive with TO or ING, with a change of meaning:
- I was reading. I stopped to watch TV (= I was reading. I closed my book and I started to watch TV) (Why did you stop reading? Because I wanted to watch TV)
- I stopped watching TV (= I was watching TV and then I switched the TV off and went away)
So STOP + ING means to put an end to that activity, and STOP + TO means to stop doing something because you start doing something different (purpose).

PRAYING= To pray is to talk to God.