I want to start importing content, but I don’t know where to look. Could you give me some advice or recommendations? Thanks in advance.
We have a lot of French lessons with audio and transcript in the French library of lingq.com, like also English lessons with audio in the English library and Russian lessons in the Russian library.
Don’t be in hurry to look for other websites before you use all rich resources of this website.
The simplest way is to have a look at the panel on the right when you are on the Import Lesson page (click the rectangular “Tasks” button and then Import Lesson - as if you didn’t know how to do it! :)). There are masses of sites to choose from.
Thank you for reminding me of that option, I completely forgot about it! 
I enjoyed this website very much, but then I got myself into futile looking for an interesting content of my level… There are just a few left that are just mildly interesting, but they are too hard. I will, though, finish courses with these lessons, I changed my mind, but very soon I will look for things to import.