Coursera is a great site for learning and understanding any type of topics . There are lots of topic which you can learn on it.
There are photography, engineering, science and computers which you can take courses from very professional teachers who are very nice and tell every topic very clearly.
It also has a app which has a very neat and user friendly interface.
The best thing is that the courses are absolutely free and have no hidden cost.
It is a very nice learning program for those who want to understand topics practically.
This is a great site and you should must check out it!