Hi,

First of all,you must have basic fundamental computer and programming knowledge.For this you may refer to Youtube where their is a lot of good content on Computer programming from basic to advanced.If you want to do a certificate course in Computer knowledge,then you may enroll in online course in Coursera or Udemy platform where courses are quite good in terms of knowledge,but these are paid courses.

Other free websites to refer are GeeksforGeeks(quite a good platform for beginners to advanced).

Remember:While taking any computer related course,you must implement the programs on your own and practice a lot for better understanding.

Hope this helps.