Is trolling when you cast out a rattle trap/rapala lure and slowly boat around a lake? I see people using downriggers/etc is that particularly needed?
yes thats trolling. depending on the fish your targeting the lure varies. ex small rapala for trout, plugs for salmon. spoons for salmon, etc

downriggers are not necessary but very helpful. they can get your weight down lower depth. and also can keep the lure down at a specific depth, for ex always around 50 feet down. where without it your left to estimate guess, a second a ft or whatever it is. and it can bounce around based on water conditions, boat speed, etc
go on google and search out "Buck Perry , spoon plugging "
he was the first bass fisherman who originally targeted bass at specific depths via trolling .
I think he used metal spoons that worked similar to deep crank baits .
I think most of the older articles were based on his success trolling deep in summer time on
larger impoundments .
tight lines ,
I remember trolling for trout at Chabot when my kids were little. They loved riding in the boat while we trolled with flashers and small spoons. Great way of getting your kids interested in fishing rather than sitting on the bank waiting for a fish to pass by your bait.

Now I learning about trolling all over again from my son-in-law side which all they do is troll for Stripers in the Delta. Just bought a line counter reel, spooled it up with lead core and waiting for my leadcore rod.
I see maybe I will try several lures running different depths since I will be guessing lol gonna hit up del Valle again this Sunday! I have a kimchi minnow that run 20 ft plus some smaller cranks
Not sure what you will be fishing for, but you could also try trolling with Kastmasters for some trout. Could even get striper with it.
It seems from the fish reports recently, the narrows have been the go to spot. Will probably only troll the first half, and spend the rest of the day hunting for bass!!