To apply for a Singapore student visa, you'll need an offer letter from a higher educational institution in Singapore. Students who have the offer or acceptance letter can apply for a student pass which is required to be eligible to stay in Singapore during their course duration. 

You can get the Student Pass Application from the Immigration Checkpoint Authority (ICA) of the Government of Singapore. But to get an S pass, the university that you have chosen to study at must register you on the online portal Student Pass Online Application and Registration (SOLAR). The student pass is generally valid for the duration of the course and the university that the students choose to study in might sometimes apply on behalf of the student for his/her S pass.