Ranked ladders and Seasons have not yet been implemented in-game, however this full feature set is coming. In the meantime, the Quick Match feature calculates your player score (ELO) and uses this information to match you against the best opponent.
Track your progress here: https://www.ageofempires.com/stats/ageiv.
Q: I've played a match. Why is my name not on the Leaderboard?
A: You'll need to complete 10 qualifying matches for your initial ELO calculation and placement on the Leaderboard. After you've completed those matches, you should see your name on the Leaderboard.
Q: Does the Leaderboard update instantaneously?
A: No, you may notice a delay of up to an hour.