Good luck with it !

On the left hand side you have 80 bass buttons arranged in 16 rows of 5 buttons each.
Each row (beginning nearest to the bellows)
contains a counterbass button (a note a " third" higher than that of the relevant fundamental bass row of the same key), a fundamental bass button, a major chord button for that key, a minor chord, and a 7th chord button.
Starting with the distinctly brownish button, which is your "C" fundamental bass, going up (skywards), the rows are arranged according to the "circle of fifths", so the key of C, G, D, A, E etc.
Going down, they proceed by "fourths", so key of F, key of B flat, etc .
Google "Stradella bases for accordion" and "circle of fifths", for more details.

A good printed introductory accordion course would help.
Here's an introduction to the bases:
en.wikipedia.org
Your's has only the first 5 buttons per row, but that's OK! ( There's a workaround for the missing 6th button)

And here:
What is the circle of fiths? In this post, we'll explain what it is, why it's important, and two interesting ways you can use the chart in your own music.
splice.com