To create a free and paid-tier community, you should enable the "Upsells" feature in the Monetization section. This will allow non-paying members to upgrade and access locked community sections.
If you want to have a free tier and two paid tiers, you only need to create two tiers, as the non-paying members will automatically be in the free tier.
When non-paying members purchase an upsell, they will be automatically moved to the paid tier. Additionally, members can upgrade or downgrade between tiers at any time.