The best way of learning arpeggios is to remember the pattern they form on the fretboard. The numbers 2, 1 and 4 indicate which left hand finger to use.
Each chord type has its own pattern of notes that can be moved up and down the fretboard or across the strings. The most common pattern for a major chord arpeggio;
If you play this same pattern starting at the 3rd fret of the second string (D string) the root note will be F. Therefore you are playing an F major chord arpeggio.
If the F major chord arpeggio is moved up two frets it becomes a G major chord arpeggio.
This G major arpeggio introduces a new D note on the 7th fret of the G string.