Simply search your on demand learning "course/subject". Then you can get a Mentor lists according to your course/subject. After that choose your perfect Mentor from the lists.
After choosing Mentor you can call him/her to fix date, time and also a place to meet. On the selected date you will meet with Mentor & star learning your course/subject.
After finishing your learning you have to pay his/her payment. Every Mentor has a profile with hourly charge rate. So you will pay according Mentor's Charge rate.