Step 1 - Online application
You only need to submit a CV. Got an email a few weeks later with the interview schedule, you can book your interview for any given date.
Step 2 - 1st interview
Once you arrive, they do a short presentation explaining you what the job entails and what functions you can choose from (Account Management, Sales, Tech, People Operations - I went for AM). Then, you present the Powerpoint you prepared (do it with passion), then you do 4 tests - a logical, a numerical, one on the handbook and one on the company and what they do (you can prepare for this by reading the website). Then you have a 15-minute laid back conversation with one of the employees, it's more of a discussion than an interview.
The tests are different from any other company tests, the numerical is basically GCSE maths (diameters, surfaces, angles etc) and the logical has a variety of questions from simple logic to verbal exercises. Brush up on the math, otherwise you'll be in trouble and most importantly READ THE HANDBOOK.
Step 3 - 2nd interview
For Account Management, you will first need to do an Excel practical with one of the Brainlabbers. They will walk you through the basics of Adwords account management, explaining clicks/costs/max CPC etc. Then you will have to do a few basic calculations (SUM function) to get a few datapoints and then produce 3 graphs from these - very straightforward with basic Excel skills and you will also be shown how to do there. Also, if you have any questions, they are happy to help. Then a couple of hypothetical questions like how does one of the variables change in response of raising the advertising budget etc, make sure you can back up any argument you make.
After these, you will have 2 10-min interviews, one about career motivations, CV and work experience and one about you as a person and what kind of people you like hanging out with. You will also have to explain something that can be a thing you learnt at uni or a sport you did.
I hope this helps, good luck!