If you are not a big fan of football, It is quite a complex structure. However, can explain to you in a simple way about the football system that we can divide football matches into 2 major systems as follows:
Domestic European football league, there will be a different competition structure for different leagues in the country. Which often have a similar structure, divided by divisions and the number of clubs in each country
European Cup Football or UEFA Champions League Football is a football cup that is not related to the domestic football league in any way. by the European Football Federation will grant the right to represent clubs from the leagues of each country according to different conditions