Take a payment
Open the Collect tab.
Enter the Amount, add a Tip if there is one, and you can use Custom tip for an amount that is not one of the presets. The button names the total it is about to take, so you are always confirming a figure you can see. Choose a different method switches between charging a card, sending a pay link, and recording cash.
Add a Note (optional) for anything worth remembering.
Afterwards it confirms with "Receipt logged" and tells you where it went: this shows up under Reports as collected this month.