Is it natural to feel like i forget some of the lessons i learn and some of the functions i learn?
And should i learn as long as i want or is there a maximum number of lessons to do a day in order not to forgot what i learnt?
It is totally normal to forget, you are not expected to remember everything. If you don’t remember something it is good practice to start searching documentation (you can just google it, one of the first results should be from the MDN - Mozilla Developers Network, or else check stackoverflow threads, and whatever else seems interesting)