Seasons are a time period during which players can gather trophies by winning matches competitively and climb the season Leaderboard. The season usually spans through multiple weeks.
Season Challenges
Players can complete Challenges to gain Season Tokens. Season Challenges are available only during each Season and can be completed in any game mode.

Daily Challenges:
Daily challenges refresh every weekday and are random for each player. You can only complete them on the day they appear.

Weekly Challenges:
Weekly challenges are the same for everyone and you can complete them at any time during the season. (Weekly challenges will be available as soon as you finish the entire tutorial)

You can also see and continue to work on the previous week's weekly challenges.
Keep in mind that the token bar moves once the challenge is claimed, not when it’s completed. Once the token bar is filled, a reward will be available to claim.
Season Rewards
Once you claim a challenge, the token bar on the top right will fill with the number of tokens claimed.

Once you have gathered enough tokens in the totalizer you'll be able to claim a reward from the following:
Weapon skins and tints
You can win weapon skins and tint for your superstars during the season. To equip it, simply head over to the superstars menu, tap the superstar you want to edit and select the weapon icon at the bottom. From there, simply equip the desired skin.
Profile avatars
You can change your avatar to a season one you have won by tapping on it in the home screen, heading to the profile tab and tapping the avatar there.
Season frames
These frames can be seen around your avatar in the post-match screens.
Rumble Coins
They will be added to your balance when you claim them.
Season Stats
You can see them in the post-match screens if you're MVP or one of the 3 players with the most changes to their stats during that match.
You can also see them by tapping in your avatar in the home screen and heading to the stats tab. In this tab you can check all the stats you unlocked in each season for each of your superstars (on the right side), as well as lifetime stats from all game modes (on the left side).
Please note Season rewards are currently only available to win and purchase while that season is ongoing.
There are also ranked rewards which you can get based on your rank during the last season. You can read all about them here.