Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
27 teams (European national domestic league champions, plus the then current title holders), playing in a tournament system, played knock-out rounds on a home and away basis. The aggregate score of both games decided the winner.
The eight teams qualified for the quarterfinals were divided into two groups of four. Every team played against the other three in its group in consecutive home-and-away matches, so that every two of these games counted as a single win or defeat (point difference being a decisive factor there). In case of a tie between two or more teams after the group stage, the following criteria were used: 1) one-to-one games between the teams; 2) basket average; 3) individual wins and defeats.
The group winners and the runners-up of the Quarterfinal Group Stage qualified for the semifinals. The final was played at a predetermined venue.