Yes, that’s right 
It is really easy to do - just sign up for an account here: https://parcel.royalmail.com/
Then you might want to check out this thread for help with integrating your Folksy shop: Royal Mail Click & Drop - ready to test
You can get fancy printers to print out proper labels for your packages but I’ve never bothered - just print them (double sided gets you two labels per sheet of A4) on the home printer, cut them out and sellotape them on. It’s particularly fab that you can then just drop them at the post office and get your usual proof of posting without messing about at the counter buying the postage. It isn’t ideal that the post office doesn’t get any kind of commission for handling the package, but things going in that direction is pretty inevitable. You can also drop your packages straight into the post box if you prefer, or have them picked up by postie, although there’s now a small cost for that