Alright so I’m not new to Halo, but I am new to how the ranking system or REQ system that Halo 5 works in. Generally speaking I’ve never dabbled much with games that use a REQ system anyways aside from WoT and that didn’t last long. Can someone explain this REQ system to this dummy?
It’s pretty simple. You earn REQ points from matches, you get more if you perform better or if your team wins. You can also use REQ boosts. You can open packs in order to get REQs (Requisitions) which come in the form on customisation items (armour, helmets, visors, stances, assassinations, emblems, weapon skins, armour mods and loadout weapons ) or usable items (weapons, vehicles, powerups and XP/RP boosts). You can also sell usable items to recieve a partial REQ refund. Weapons and vehicles can only be redeemed in Warzone, and require REQ energy, but that’s a whole other subject.
The packs are Bronze (no garuntee of a permanent REQ, with some low level usable REQS) Silver (2/3 mid tier permanent REQS, mid tier usable REQs) and Gold (2/3 high tier REQS, lots of varied usable REQS)
You play games to earn REQ points. Save up enough to buy REQ packs. There are three types of pack: Bronze, Silver, Gold (with the exception of the occasional promotional pack). Bronze packs offer Common REQ’s, aka carbines, mongooses, level one power ups, etc. Silver packs offer 2 permanent unlocks and a selection of other REQ’s. It’s advised to buy these packs until you’ve unlocked everything of common to rare rarity, after that you buy Gold packs. You can also sell individual REQ’s for more points.
Permanent REQ’s include armour, helmets, visors, loadout weapons for Warzone, weapon/vehicle clearances (explained a bit further in my post), weapon skins, stances, assassinations and other customisation options. Weapon REQ’s come with each pack, and you’ll get some “Weapon clearance” REQ’s, which give you several of one type of weapon, which also adds that type of weapon into the mix when unlocking other packs.
For example, you buy a silver pack and you get a helmet and a Blood of Suban (carbine variant). You’ll get the helmet, a handful of Blood of Suban’s and you’ll also get a plethora of weapons, vehicles and power ups to use in Warzone.
I hope i described it as well as you were hoping. Feel free to ask if you have questions. 
Oh, and there’s also XP boosts, REQ point boosts and Gambit boosts to unlock. The first two are fairly self-explainatory, but Gambit boosts basically offer either REQ points or XP depending on how you perform in-game. You could for example get a Gambit Assist boost, which would give you additional REQ/XP depending on how many assists you get in a game compared to other players.
You earn Req Points (RP) when you complete a match. You then use the RP you collected to buy Req packs. When you open the packs, you’ll randomly get customizations, weapon and vehicles certifications, loadouts gear, boosts, and single-use cards. You use the loadout gear and cards in Warzone. Any other questions?
Xp basically useless. (If you don’t care about rank)
Req points are used to buy Req packs.
Start with bronze and once you have all the common stuff (you will start to get points back if you open a bronze pack)
Now you can start on silver’s, from those you’ll get uncommon and rares.
Once you finish the long grind, you can now finally start the even longer gold grind.
The reason you go bronze > silver > gold is because of effeciency. You buy a gold pack before finishing the others you will get uncommons rares and commons. Doing so is a waste of points and time.
Good luck and Welcome to Halo 5.
Just for starters, start by opening bronze packs only. Then, silvers. You will know when to stop because you will start to get cards that give you REQ points. Finally, go to golds. Same deal with them. After gold, you can deal with specialty REQ packs.
Hope you found this helpful!
-Sly
shoumd give you some good information on what it is and how it works.