Questions on "end game"

[Wubsie]

What I know that I need to do is "gear up" - Just focusing on leveling through outdoor quests the last few weeks has me substantially lower than other people my level, so certainly at 120 I will be very gimpy. What is the best way to really getting the higher end gear for my teams?

You can gain gear through a number of sources. Some of the easier ones ways will include world quests, which will appear on your map once you unlock them, world bosses that can be beaten for a chance at a gear drop once per week, zone invasions, and normal/heroic difficulty dungeons and so forth.

As you'd expect, the harder the content, the better the rewards. The top rewards would generally come from mythic+ dungeons, as raiding, especially with multiple toons in a current raid tier is usually out of the question, or at least very very hard to find an accommodating group for...

I see a lot of people talking about keys, M+ levels, dailies, weekly chests ... none of which I have the slightest idea what they really are because I haven't done any of them.... so I am like George Costanza and writing things off on his taxes. I say all those but really no idea what they are or how to do them. Are they separate things or all the same thing? I just know asking this question in Blizzard forums and asking here will yield entirely different results, so asking here

Keys and Mythic + refer to the same thing really. Mythic+ is an ever increasing difficulty system for dungeons.

After you complete a mythic dungeon for the first time that week, you can a Mythic+ keystone (unless you have one already. That then will allow you to complete another random dungeon on a slightly higher difficulty (+3 for example). Mythic+ Keystone runs have a time limit. If you manage to clear the dungeon in time, you gain a higher key to another dungeon. Based on how fast the clear was, the next one will be 1-3 "levels" higher. Contrast to normal dungeons, keystone runs do not drop loot on each boss, but you have a chance on loot upon completing the full instance. Again, the level of the key and how fast you completed it define the level of loot and how many rolls you get, in the form of treasure chests that might contain loot. The difficulty scales up fairly quickly and just brute force will not get you far. At certain difficulty intervals new mechanics are also introduced to the dungeon. E.g, each time a mob dies, other mobs you are in combat with will gain 20% increased health and damage. Or explosive orbs randomly appear and need to be killed before they explode, etcetc. Based on the highest keystone you complete before the weekly reset, you gain a weekly reward chest with some very, very nice rewards. If you can manage decent keystone levels, this is where you might expect to to find some of the highest level items you can get your hands on. although with the current corruption mechanics, the item level is sometimes not as important as just getting lucky and getting the right corruption thingymabob on your loot.

Dailies are just quests that can be completed daily. The term is a bit misleading as it previously refered to a single quest that could be done each day, usually to grind rep, tokens that were currency for items or whatever else reward. Now there are also a bunch of quests that appear on your map in the open world that give different rewards. Doing these quests for the right factions will complete an emissary quest, which you get one of per day. That will also appear on your map once you've unlocked world quests.