Well, "golden keys" or Treasure Keys are a semi-rare drop that allows you to open Treasure Chests at the end of Prison of Elders. Treasure Chests have a chance to hold Legendaries and Exotics are are often kinda like a pinata of stuff.

Prison of Elders itself is the new, wave-based PvE co-op arena. Some people don't like it, but overall I think it's one of the best things to come to Destiny. It's lots of fun and can be achieved without needing a crap-ton of friends and hours of time commitment.

Trials of Osiris is the elimination style PvP event that comes every weekend. Your power level comes into play here just like Iron Banner. But this is 3v3 elimination and can be a real, real pain in the ass if you get on a losing streak. It's incredibly fun, and incredibly awful at the same time. Bring either unbreakable friendships with you. Or friendships you're okay with losing. :P

Honesty I'm in the dark. I've heard something about golden keys, but don't know what they are. I've heard about trials and the prison of elders, but I don't know which is which our what they do.

I know, search is your friend. Just looking for a condensed version of where to start.

Prison of Elders:

• big new PvE thing in the Reef
  
• House of Wolves required
  
• fireteams of 3
  
• one of five (or so) different combinations of enemies each week
  
• lowest level is matchmade
  
• features new mechanics
  
• treasure keys are used when playing this
  
• this is the only way to increase House of Judgment reputation and buy stuff from Variks in the Reef

Trials of Osiris:

• new PvP thing
  
• House of Wolves required
  
• DLC required
  
• fireteams of 3
  
• runs Friday morning through Monday night
  
• one map a week
  
• uses the Elimination gametype-- deathmatch/slayer that ends a round when a team is all dead at the same time
  
• if everyone survives to the end a control point appears, first to take it wins
  
• each match has 5 rounds (or maybe it's 5 rounds to win?)
  
• attack, defense, and player level matter like in Iron Banner
  
• enemies are matchmade but fireteams must be assembled manually
  
• access must be bought from Brother Vance in the Reef
  
• wins give you access to gear that Brother Vance sells (which is of course Egyptian-themed)
  
• too many losses and you'll need to buy access again
  
• Brother Vance also sells items that give you free wins, forgive losses, etc. (these take "passage coins" which can be earned a bunch of ways)

The Wolf hunt:

• the House of Wolves rebelled against the Queen of the Reef, now you get to hunt them
  
• no DLC required for the events or their bounties
  
• overworld events happen in select areas on a similar scale of time and space as the Blades of Crota
  
• Blades of Crota events don't happen any more, sadly
  
• the overworld events are marked by the text "A pack of Wolves is prowling"
  
• a Skiff drops in when this happens; killing its passengers triggers more, ending in a named mini-boss
  
• Petra Venj in the Reef gives out bounties for completing these events
  
• completing an event spawns an "ether chest" somewhere in the area and gives you a countdown to when it despawns
  
• ether chests can give glimmer, materials, special ammo synths, treasure keys, and the various tokens that can be redeemed with Variks in the Reef

Weapons and armor:

• new legendaries and all (recent?) past and future Iron Banner weapons can be "reforged" with the Gunsmith, resetting their progression and giving new perks
  
• all legendary and exotic gear can have its peak attack or defense increased by "ascending" it
  
• legendaries use etheric light (new legendary-tier material) to ascend, exotics use an extra exotic shard
  
• new legendaries don't take shards or energy and use less of the other upgrade materials
  
• new gear only has perk nodes and usually an ascension node (some gear has no ascension node and starts at maximum attack/defense)
  
• new gear breaks down into glimmer, weapon/armor parts, and motes of light
  
• ascension, reforging, and most of the new gear can be had without the DLC

Misc.:

• maps from The Dark Below can be played on by anyone
  
• the rotational playlists now last all week instead of being restricted to the weekend
  
• your vault has more space
  
• the Speaker exchanges certain types of materials and currency for each other
  
• Xur doesn't upgrade stuff since you can do that now, but he does exchange strange coins for motes of light
  
• the beginning area of the game is open and has new and old stuff added in
  
• the Reef has a new social space featuring the characters mentioned above plus a bounty bot, a postmaster, the vault (the same one as the Tower), occasionally Xur, and a new Cryptarch who is a glorious English Awoken asshole
  
• the Tower has a new ball and a jukebox, which are also glorious (but not English, except for some song snippets by a certain person)
  
• Hunters officially glow with beautiful energy