Leagues are given coefficients, too. The leagues with the highest coefficient are given more automatic spots in the competition, while lower-ranked leagues have fewer.
England have four automatic spots in the Champions League, as the league with the most coefficient in Europe. Scotland, for example, only have one automatic spot in the Champions League group stage as a weaker league.
Similar to the FA Cup, there are some nations in which clubs will have to endure qualifying rounds, with the lowest-ranked leagues having to start fixtures much earlier and clubs from other nations, such as France or Austria, coming into the competition later.
After England, the highest-ranked leagues are Spain, Germany, Italy, France, Netherlands, Portugal and then Scotland.