Sending a parcel is similar: you can prepare a shipping label at home and print it out. When you arrive at a locker, you just scan label's barcode, a door opens, and you pop your parcel in there. Or you can prepare the label at the parcel machine, it will print out a sticker for your parcel. Stick it on, scan the code, door opens, put your parcel there.
A standard parcel locker looks like this: https://i.imgur.com/X5Gj4JQ.jpg
Different size doors are for small / medium / large parcels. Center section has touchscreen, payment card reader, barcode scanner and a printer for shipping labels and receipts.
Such parcel lockers have been around for approximately 15 years, but usage exploded somewhat later.