When you get into the McDonald’s just walk up to the counter to one of the staff working on the tills and let them know you’re there for an interview, they will let their manager know and you will be asked to take a seat in the restaurant whilst you wait for the manager to come over to you, the interview will be conducted wherever you’re sat in the restaurant so make sure you get a good seat.
You’ll be asked general questions like “Who is your inspiration?” “Why do you want to work at McDonalds?” and “What’s more important in fast food, fast or friendly service?” - hint: for the last question they’ll be looking for an answer along the lines of “Friendly service is more important as people are more likely to tolerate waiting if they receive friendly service”. You’ll also be asked about your availability- what days you’ll be able to work and during which times, as well as how many hours per week you would like to work - generally weekend work is what they’re most after as these are the busiest times.
After you’ve been asked the questions you should be asked on to the shop floor to work for about 5-10 minutes, if the McDonald’s you’ve applied to has a drive-thru then you’ll most likely just be handing food, drinks, straws and napkins out of the window to customers, someone will be with you giving you all of the food and drinks so it is pretty straightforward. When you’re doing this you will be being assessed by a check sheet, make sure you do things like maintaining eye-contact with the customer and speaking loudly. When the customer gets to the window be sure to greet them, and when they leave be sure to say thanks and to “have a nice day”, they are mainly assessing your ability to communicate clearly and in a friendly manner at this stage. I can’t comment however for exactly what happens if the restaurant you’ve applied to doesn’t have a drive-thru though it is probably a similar thing but on the till.
If you’re successful you should hear back from them within a week or so inviting you to a welcome meeting, during which you will be playing a custom McDonalds board game with other people who have been successful at the interview, you basically take turns rolling a dice and landing on different squares on the board, when you land on a square you get asked general questions about McDonald’s, nothing too difficult or important. Yes this board game is an actual thing and no, it is not a fun game... At the welcome meeting they’ll also take your sizing for the uniform as well as your bank account details and national insurance number so they can pay you.
Good luck at your interview, I worked at McDonald’s part-time while I was in college, and though I can’t say I enjoyed the job, I still consider it a good way to start out working and there aren’t many jobs more flexible than McDonalds if you’re working part-time, which is great if you’re in college or have other commitments.