No Need to feel like a idiot. Because the Terms we use have sometimes Blurred Meanings.
In most cases...
RDA = Rebuildable Dripping Atomizer with No Tank. Just a Well to hold the Wick and a small amount of e-Liquid. You put the e-Liquid in by Dripping 4 or 5 Drops onto the Coil thru the Drip Tip. Then after 4 or 5 Hits, you have to Drip some more e-Liquid into the RDA or it will run dry.
RTA = Rebuildable Tank Atomizer. Has a Tank to Hold e-Liquid. It can't use replaceable Coil Heads. And the Rebuildable Deck is Fixed to the Atomizer Base.
Coil Head Tank. Has a Tank to hold e-Liquid. But it wasn't designed to be Rebuilt. When the Coil Head gets old, you replace the Entire Coil Head.
RBA Section. A Rebuildable Coil Head that can be used in a Tank that either tanks Coil Heads or a RBA Section. A good example of a Tank that can use either a Coil Head or an RBA Section is the Kanger SubTank or TopTank Mini.
In this picture, the Coil Head is on the Far Left. And the RBA Section is next to it.
Hears a Close Up of the RBA Section...
Coil Head tanks (IMO) can give Good Hits. But not as Good (on average) to a RTA or a Tank running an RBA Section. But they are Very Easy to Use. Just Swap Out the Coil Head when it get Old with a New One. But this can Also be kinda Expensive.
RTA Tanks and Coil Head Tanks using an RBA Section (IMO) give Better Hits. And are MUCH Cheaper to use. You can also Fine Tune the Hit you get by the type of Coil Build you put into them.
RDA's (IMO) give the Best Hit. But are kinda a PITA in that they do Not have a Tank. So you Constantly have to Drip e-Liquid into them. They also are somewhat Awkward as on an On-the-Go setup. Because you need to Carry a Bottle to drip with. And they can be a Major Distraction while Driving.
That is why "Squonking" has become so Popular with Many People. Because a Squonk Mod has a Built In Bottle of e-Liquid in the Mod. And when the e-Liquid Bottle is Squeezed, the e-Liquid if Forced up a Tube thru a tube into a Hollow 510 Connection in the RDA. So you Don't need to have a Dripper Bottle and Drip e-Liquid into the RDA thru the Drip Tip.
For someone just starting out, a Coil Head Tank is not bad call. Because they are so easy to use and can be Less Frustrating sometimes.
For someone who is Past the Initial Pain of quitting smoking, a RTA or Tank with a RBA Section or an RDA is a Good thing to Try. Because (IMO) they hit better. And Learning to Build Coils is Easier when you are Not going thru Smoking Withdraws.
I kinda Glazed over some things. And there might be some Exceptions to all this. But for the Most Part I hope this gives you a Better Idea of what is out there.