First lesson? You just opened it by asking for the meaning of the word "certain"
From Dictionary.com
1. free from doubt or reservation; confident; sure: "I am certain he will come."
2. destined; sure to happen (usually fol. by an infinitive): "He is certain to be there."
3. inevitable; bound to come: "They realized then that war was certain."
4. established as true or sure; unquestionable; indisputable: "It is certain that he tried."
5. fixed; agreed upon; settled: "on a certain day"; "for a certain amount."
6. definite or particular, but not named or specified: "A certain person phoned. He had a certain charm."
7. that may be depended on; trustworthy; unfailing; reliable: "His aim was certain."
8. some though not much: "a certain reluctance."
PS: I took the liberty of changing your post. Have a look at this:
So, what
are the first lessons? By the way, what
does 'certain'
mean?
So, what
is the first lesson? By the way, what
does 'certain'
mean?