I have decided to apply to PhD studies and in one part it says that my CV should contain: "Study curriculum with rankings". What does that mean? because they are also asking me to submit my studies transcripts.
Study curriculum means the list of titles of courses/subjects and their contents, credits, and so on. In other words, the syllabus.
The term 'Ranking' is generally associated with the institution. Probably they are asking for the ranking of the university/college you attended. 'Ranking' may also imply your position in the class of X number of students. It may also simply mean the semester-wise serial number of courses.
Do these instructions come from an institution in an English-speaking country? If this came from an university in my homeland, I'd interpret it as "list of all courses taken with grades", clumsily translated into English. Besides that, it's not unusual to ask for this kind of information in when applying for a PhD (at least in Italy).