About the volumen of the sound, you can have a piano or a forte sound, a soft or loud sound, in a volumen of 1 to 10 "Mezzoforte" will be about 6, more or less in the middle, not too loud, not too soft. Mezzopiano means "Middle Loud". Mezzoforte is a little bit louder than Mezzopiano.
This group of 4 eighth notes with a beam, is very popular in music, you will see it a lot, is much easier to read then if you have 4 separated notes, with a little flag.
There are many time signatures, in a 2/4 time signature, you need two counts, each count must be 1/4. So two counts is 2 quarter notes, or 4 eighth notes.
Andante means "Walking" this tempo is at a walking speed, A little bit slower than the Happy or Allegro tempo, but faster then the Adagio or Slow tempo. Remember that all these tempos are more or less, you need to feel the tempo, because you don't have the metronome with you all the time, you need to feel the tempo.
Enharmonic is a term for the same sound with a different name. Like if you have two notes, they have different name but they sound the same, tose are enharmonic notes.
Try this test to see how much you know so far. You need to know 10 symbols in a row with no mistakes.