This is probably a subject to the FAQ...
Alliances is not described in detalis in the manual...
But what is it in for me to joining an alliance?
And the 0.8 % of my ticket income... Who is getteing this and to what is it used?
Fee is used in general administrative costs of the alliance, no airline gets it.
Benefits of alliance membership are described on the alliance section front page: https://www.airwaysim.com/game/Info/Alliance