You would use "less" with "than" The value A is less than B. Also, if you are modifying some adjective, use "less". "This job is less stressful." ("than some other job" is implied) If you are modifying a noun with an article ('a', 'the' or numbering it), use "lesser". In the above example, "value" is the noun being modified. "Take the lesser of the two evils" "Of the two teams, Chicago is thought to be the lesser challenge."

lesser= more less for example, a man ask you, give me less than you are giving me, then you give, then he says give me lesser( less than he asked )