Play the note D with the second finger of your right hand.
This is a half note.
Sometimes called a minim. It lasts for two counts. There are only two half notes in one measure of * time.
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.
These songs use a mixture of half and quarter notes.
Because of the * time signature, there must be a total of four counts in each measure.