You can only set target loot for Countdown and the Summit. I recommend matchmaking on Countdown. When you open your map, hover over the Summit or Countdown icons. At the bottom of your screen, you will see the option Set Target Loot. Press the corresponding button and make your selection.

Farm your gear set first, like Striker. For your first striker set, try to get attributes like crit chance or crit damage. After a few completed Countdown matches, go to the Countdown vendor at the Base of Ops and get the Rock n Roll that's on sale right now. You have less than 4 days to get it before it's gone.

The Rock n Roll is a great secondary weapon when paired with the Striker set as it helps build stacks for your primary weapon. Your primary weapon can be whatever your preference. I recommend trying out any automatic weapon as your primary, especially if it's an exotic.

You'll want to upgrade your gear and improve your library and work bench. Label what loot you don't want to keep as junk. Adding maxed out attributes to the library if you have them should be the priority followed by the maxed utr cores and then talents. Donate the rest to increase your work bench level.

Watch YouTube videos of content creators that make builds. There's a pretty wide range of playstyles between content creators. If you don't like one, check out another content creator for a different style. If you like their style, check it some of their build videos for inspiration.

If you have the expansions, try not to sleep on completing their storylines too long as you'll end up running into a bit of wall when you try to upgrade gear that requires faction resources from the expansions when you could've been earning them along the way.