You apply through the website, I uploaded my CV and a cover letter but the cover letter was optional (I'm sure they didn't read mine). The online assessment is divided into 3 parts: English, Logics, Mathematics, and then a part on your "Working style". The Logics and Mathematics parts are quite easy (even though I couldn't finish). The English part (vocabulary questions) is difficult when English is not your first langage... Then you have an online interview with typical behavioral questions.