An eSIM is just a physical SIM that has gone digital. Instead of you physically inserting a SIM into your phone to join the Mint network, you install an eSIM onto your phone/device. It means you don’t have to wait for your SIM to be delivered, you can activate straight after purchase.
If you are new to Mint, and have an unlocked, eligible device you can choose eSIM at time of purchase.
If you are an existing Mint customer, then log into the Mint app, head to Settings > SIM > Replacement SIM. Right now eSIMs are only available on selected iPhone devices (iPhone XS, XS Max, XR, any iPhone 11, any iPhone 12, or the latest iPhone SE).