This is very simple stuff. Once you understand the easy theory behind it you’ll be able to transpose anything you want.
Just understand that you play an Eb alto. It’s called an Eb alto because when you play a C on it, that C is an Eb on the piano.
If you look at the keyboard you’ll see that the difference between a C and an Eb is a minor 3rd, or 3 semi-tones (C#, D, Eb)
Now look at the music you pointed out, it’s in A minor. If you want to transpose it to alto you must be a minor 3rd below, so count down 3 semi-tones from A (G#, G, F#) …you’ll be playing it in F# on your alto so it matches the A on the piano.
If you are only going to play it by yourself you don’t need to transpose it at all, just read the piano music and play it in A.
