How do I ask doubts and clear it?

Hi Arjun, if you have questions about anything discussed in videos or articles or video talk throughs you should be able to ask questions under the teaching material in a box with he title Ask a question. 

In case you don't see this box you may be on a restricted or child account. If so you cannot write questions yourself on Khan Academy, you must get an adult to ask them for you.

If your question is a homework question or does not have anything to do with the video or article, however, it is likely to be removed. Questions that aren't relevant to the subject of the teaching material are likely to mess with student concentration - just as in a regular class.

(volunteer Star guide)