It is pronounced as "four two beats", "four three beats" and "four four beats" respectively. These three beats all take the quarter note as a beat, which is the denominator. Molecules represent the number of beats per bar.
The law of the strength of 2/4 beat is strong, weak | strong, weak |, and it goes on and on, with one strong and one weak appearing alternately. You can think of it as the slogan of the playground "Let's go" and "one two | one zero |" (I think so).
3/4 beats are strong, weak and weak | strong, weak, weak, one strong and two weak alternately, suitable for relaxed music.
The 4/4 beat is a combination of two 2/4 beats, and the law of strength is strong, weak, sub-strong, weak | strong, weak, sub-strong, weak |, which is suitable for stable timbre.
I'm not sure what you said about 8/3. I just play a musical instrument, so I know some basic hopes that I can help you.