On a Mollie subscription the customer never enters a card, and the money is collected from their bank account instead. You manage it on its own page in the app, and everything depends on the SEPA Direct Debit mandate their first payment leaves behind.
The customer checks out with iDEAL | Wero or Bancontact. Until Mollie confirms the mandate, the subscription sits at Pending mandate. Confirmation can take a few days; the status updates by itself. If the mandate never becomes valid, the subscription ends up at Mandate failed and nothing is charged.
On each billing date the app charges the mandate through your Mollie account. Mollie SEPA Direct Debit is euro only, so these subscriptions are always in EUR. If the first order is in another currency, the customer is still charged for that order, but no subscription is created and nothing appears in the list. A store that does not sell in euro gets no Mollie subscriptions at all.
On the bank statement the charge shows a default description with the subscription number, unless you set your own text in Payment description on bank statements.
SEPA can take several days to settle. With When the charge is created (recommended) the Shopify order appears on the billing day so you can ship. With Only after the payment is paid you wait for the money, which is safer but delays delivery. Either way there is one order per billing cycle.

Most of the app behaves the same on both engines. The customer account portal, add-ons, product swaps, the cancellation flow with its survey and retention offer, gifts and the renewal reminder all work here too. Three things do not.
Discount ramps are flattened. A plan that lowers or raises the discount after a number of payments charges the later price from the first renewal on. Only the first order, the one paid at checkout, uses the starting price.
Two portal switches do nothing. Delivery method and shipping option cannot be changed by a Mollie customer, because those belong to a Shopify subscription contract. Every other switch on the customer portal settings page applies.
Changing how they pay means a new mandate. There is no stored card to swap. A customer changing their payment details authorises a fresh SEPA mandate instead, which is what the Edit payment info switch drives here.
Read Read the Mollie subscriptions page to interpret the statuses and the list of charges.
Read When a payment fails: retries and dunning for the SEPA retry rules.
Stuck on any of this? Open the chat in the bottom right corner of the app and we will help you set it up.