The Outlaw Pass in Red Dead Online is a new system that allows you to level up and earn rewards as you go. Similar to a Battle Pass from other games, the Outlaw Pass has 100 levels to complete which will earn you different rewards at each tier of the pass. The outlaw pass requires that you use in-game gold bar currency to purchase it. You will need quite a bit of gold stored up to purchase the Outlaw Pass, it currently costs 40 Gold Bars.
The Outlaw Pass can be purchased in a couple of ways. The first is through the Catalogue menu. Simply open the Catalogue and go to the Wheeler Rawson Club section. On the second page you will find the Outlaw Pass can be purchased here. The second place you can purchase the Outlaw Pass is in the Progress Menu. Simply open the pause menu and scroll to Progress. The select your first option for Club Rewards.
In this page you will find all of the rewards for the Outlaw Pass. Simply use the d-pad to navigate to the lower section where items have a gold lock on them. There you can find more details about the Outlaw Pass and the ability to purchase the pass directly.
Of course you will need gold to make the purchase. If you are a little short on gold, try this guide for getting gold in Red Dead Online.