The note D is written in the space under the staff.
Play the note D with the second finger of you right hand. Place a D sticker on all the D notes of the keyboard.
This is a half note, sometimes called a minim. It lasts for two beats. There are only two half notes in one bar of * time.
This song contains four bars of half notes using C and D.
The big numbers 1 and 3 tell you to play the note. The small numbers 2 and 4 tell you to hold until the next note.
The next two songs use a mixture of half and quarter notes. Because of the * time signature, there must be a total of four beats in each bar.