Anyone credit card savvy?

[FrenchMartiniAhh]

Looking for a bit of advice, I have recently been accepted and issued with a Vanquis Credit Builder card.

I never use credit anymore and I have only applied because I need to build credit. I don't understand what all the terms mean in the booklet they've sent.

The monthly purchase fee is 2.9% - does this mean any purchase I make an additional 2.9% will be added? I made a transaction of £20 and paid it straight off. It shows as paid in full but I didn't pay any additional fee?

Sorry I sound dense, I want to know how it all works.

You normally get an interest free period so if you pay the full balance by the due date then no interest is added.

The 2.9% being the interest we are assuming! So if the 2.9% is the interest, for example, in April, you use the card, purchasing £110 of goods. Your bill comes on the 1st of May, due on the 15th, with a minimum payment of £10. You pay £110 before the 15th. Brilliant! You owe no interest.
If you just make the minimum payment of £10 you must pay interest, at a rate of 2.9% per year (but they will apply it daily at 2.9% / 365, so in this case a few p per day). If you pay nothing before the due date then you will be hit by charges and higher interest and it gets a bit more grim.