The Create tab is where you perform all your actions on the NFTs from your stores, or from other stores where you are a minter. These actions can be thing like minting, listing, sending, burning an NFT and so on.
To access it just click on Create on the navbar.
Create Tab on Mintbase with a store selected
On the selector field (top left) you can select the store you want to create from.
You can also deploy a store clicking in New Store.