Why Lessons and not Lesson?

[tobyty]

I ran across this sentence:

"The first lessons will be about verbs, and how they are recognized and used."

Why "lessons" is plural? Is it correct to say "the first lesson will be about ..."? Does it convey different meaning?

I sometimes have a hard time deciding when to pluralize count nouns.

[Alan]

It presumably means, e.g. lessons 1-3.