To play the one finger A chord, press the A key with the third finger of your left hand, as shown in the diagram. As this chord is a one-fingered chord, the fingering is the same for all types of keyboard.
To play the fingered A chord, use the first, third and fifth fingers of your left hand, as shown on the fingered A chord diagram.
When changing between the A and F fingered chords, keep your fifth finger on the A key. When changing between the C and A fingered chords, keep your thumb on the E key.
Sometimes as in this song, there are two sharp signs after the treble clef. You do not need to learn any new notes to play this song.