As the title suggests,
How could you guys explain to someone who is new to this game, the difference between this terms: "LEAD" and "NO LEAD" a.k.a "lead 1/0"

My friend Erick can not understand this 2 methods to play this game.
and im sick of trying to get him to understand this.

any suggestions from a technical or historical point of view?

by historical I mean since when this was implemented and how improves the game experience over all ?

as always sorry for my english level.

Yeah, in a nutshell, lets assume that you have 60ms ping, so 60ms lead, which in our super hypothetical is 1 in-game meter ahead of the guy you're shooting at.

With lead, you'd have to shoot 1 meter ahead of the guy, and it would count as a hit, because when you say "I SHOT A BULLET!" the server doesn't hear you say "I SHOT A BULLET!" until 60ms later. When the SERVER hears you say "I SHOT A BULLET!" is the actual time at which the bullet goes out and tries to deal damage. So it says "Cool, you shot a bullet, let me spawn one", and then does so. But remember, because there was the time between you telling the server you shot a bullet, and it hearing you and actually spawning that bullet, in that time the guy you're aiming at has moved 60ms (1 meter) ahead. That is why (in a super simple nutshell) you have to lead.

(it's also why lead is unfair to players with high ping)

With nolead, the same stuff happens, but this time when the server hears you say "I SHOT A BULLET!" it goes, OK, you shot a bullet, let me spawn it BUT WAIT! your ping is 60ms, so lets go ahead and see where everyone was 60ms ago (because that's where they were when you sent the message, not when the server got it, which is what really matters in terms of the gameplay experience...) and lets see if this bullet would hit any of those locations. OH, it DOES?? Then we'll register a hit and call it a day.

It sounds simple, because the concept itself is very very simple. Implementing it, however, is not as simple, and requires a lot of vigorous testing and other things. The fact that we have a game where a server-side extension rather than an engine/netcode modification can simulate nolead is pretty damn impressive if you ask me. Again, it's not rocket science, but it's tedious hard work that requires not only an intimate knowledge of the inner workings of a Halo PC/CE server application, but rigorous testing and relentless tweaks to get it into working order.

Hope that was a decent ELI5

Oh Thank you!

After a few tries my friend finally got it!

and I learned a little bit more because of you, there was some thing i didnt know tho,

thank you sir! ;D