How to read it
Every note the chart covers is on the staff, lowest to highest, with its slide position underneath: 1st is all the way in, 7th is all the way out. Smaller numbers are alternate positions.
Notes with two names
A♯ and B♭ are the same note, with the same position. The chart writes the flat on the staff and the sharp name under it, so you can find either one.
When to use an alternate
Alternate positions save slide motion between notes that are far apart in their main positions. Most sit a little sharp or flat, so listen and adjust the slide.