Quote:I searched in Google a lot but did not find anything
There is a reason for that ... put simply, there is not "one way" that you can or should store "lessons", partly because a "lesson" will vary from teacher to teacher, and partly because the requirements of a "lesson" will vary immensely.
Some teachers require very little; a broad subject line is enough: "
The War of the Roses
" is enough for a well educated History teacher to begin running off endlessly about the subject. For others, this will need to be broken up into a sub list:
1 Name and symbols
2 Summary of events
3 Origins of the conflict
3.1 Disputed succession
3.1.1 House of Lancaster
3.1.2 House of York
3.2 Henry VI
4 Start of the war
5 Act of Accord
6 Death of Richard, Duke of York
7 Edward's claim to the throne
8 Yorkist triumph
9 Edward IV
10 Warwick's rebellion and the death of Henry VI
11 Richard III
12 Buckingham's revolt
13 Henry VII
source: Wars of the Roses - Wikipedia[^]
An even less trained teacher may need the whole Wikipedia article, or to read some of the thousands of books which will cover the subject!
And this applies across all subjects - IT is no different, many teachers are not IT specialists, but "teaching specialists" who have been trained to teach others (and if you don't think that is a seriously difficult skill, I strongly suggest you invest in a "trainer training" course for yourself!)
Remember the aphorism: "Those who can, do. Those who can't, teach"*
As a result you can store "lessons" in pretty much any way you need, as it will need to be seriously flexible to store "any lesson" you may be better off just using a word processor!
I'd start by looking at what you have to store and work out from that where to go next: we can't do that for you!
* And it's corollary "And those that can't teach go into politics"