Reference for the Grothendieck's standard conjectures on algebraic cycle

Question

Is there any source explaining or dealing with Grothendieck's Standard Conjectures on algebraic cycles in detail? For example, in the Wikipedia article,

1. What does "Lefschetz operator ($\Lambda$) is induced by an algebraic cycle. (Conjecture B)" mean?
2. What does "the projectors are algebraic (Conjecture C); i.e., induced by a cycle $\pi^{i} \subset X \times X$ with rational coefficients" mean?

And so on...

I would be grateful if anyone could help me.

Answer 1

I think both of your questions (and more) are well-answered by Grothendieck's original paper.