If you do not have a musical keyboard near your computer, make a copy of the mock keyboard as directed on the first page of these lessons. It will be helpful to you in learning the keyboard.
When the notes on the staff go from a line to a space or from a space to a line, we step up or down to the next note letter.
In the first measure we begin with the thumb of the right hand on the red-dotted middle C (line). Step up to D (space), then to E (line).
In the second measure, the third finger is on E (line). Step down to D (space), then back down to C (line).
This song is written in 4/4 time which means that we count 1,2,3,4 and the black note with a stem (quarter note) gets one count. The white note with a stem (half note) gets 2 counts.