

Short version is they cannot govern without a coalition partner, but they gain other rights in the parliament, such as filling important positions in the administration. When they reach 1/3 of the votes, so 33% they have a Sperrminorität, which means they can prevent changes in the constitution and also hinder new judges in the constitutional court.
Yes, he’s great data scientist. He has more stuff on his webpage, e.g. bias analysis of the different polling institutes, be sure to check it out if you like!