how should I be positive about financial support? I am accepted for the January intake.I am a fully funded student. 
I received the acceptance letter from university but the university has not sent me any financial support letter.
My supervisor just sent me a letter of financial support.
A financial support at $22K per  year from which $15K comes from Supervisor's grant money 
and the rest from internal funding available to the graduate students in our faculty in form of research and 
teaching assistantships.

Is it enough to have a financial letter from the supervisor? or Should I send the university an email and ask them to send a letter of the financial letter?

because on my personal university portal there is not any section for funding.
what should I do before starting my study? since it is really important to finance my study form very beginning. what should I write to the university and what should I ask?

Thanks in advance!
Depending upon the university, your funding may come from the department, rather than the university, and it thus would likely be the department's responsibility to send you a letter outlining where your funding comes from. (In some cases, this devolves to the faculty member.)

If you have any questions, the best place to start would be the graduate advisor or the graduate admissions officer for your program. They should know how funding letters are announced.