Every line and every space corresponds to a single note.
The blue letters correspond to the line next to them and the green letters correspond to the space next to them.
So you can look at a line or a space, follow it to the left and you can read which note is is.
If you read the letters from bottom to top, they are (A) - B - C - D - E - F - G - A - B - C - [...]
Just like a pinao where the (white) notes are layed out the same, but from left to right instead of bottom to top.
There are cases where a line or a space could potentially correspond to a flattened or sharped note (the black keys on a piano). In this case these notes are marked with a flat (b) or a sharp (#) sign. Another possibility is when you have another key signature than C/Am. In these cases the key signature will be notated with flats or sharps in the beginning of the peace and depending on the key signature some lines and spaces could correspond to a flattened or sharped note (the black keys on a piano). But you will learn later about that.