You can create a new membership from Admin > Commerce > Products. Click the +Add button, then choose Membership from the Category dropdown menu:
Membership Tiers are useful if you require that players have at least one out of a number of acceptable memberships. For example, your event(s) might require players have either an Adult Membership or a Youth membership. You can assign both of those membership products to a Gold tier, then make the event(s) require a Gold-tier membership.
To create Membership Tiers, either edit your organization's current membership product or create a new membership product. You will see an option to add Membership Tiers:
Once you've added Membership Tiers to your membership, you will see those Tiers as event requirement options (e.g. only Bronze level members may participate in this event).
Alternatively (and perhaps more commonly), you can assign a Price Point to a specific Membership Tier. The "With Membership Tier" box will appear once you've selected a Membership. For example, an admin could make an event free for Gold members and half-price for Silver members - all other registrants would be charged the full price.
Note that you will likely want to create separate Membership products for each Membership Tier.