First, don't feel bad about being "lost". That's completely normal. Fifteen months ago, I blundered in here absolutely baffled.
Fortunately, ECF has tons of folks happy to pass on what they learned. A year ago, I didn't know a 510 from a French fry. Now I DIY my own liquids and sling jargon all over.
Hang out, ask questions--even if you worry they're "dumb" questions, you'll find your corner of the rather large and sometimes intimidating world o' vape.
That said...
The products that "look like" a cig are going to disappoint. For one, their batteries are too small and under powered. I started with Blu and almost lost my mind swapping batteries constantly. A lot of start trying to find a close match to our former habit, pretty much nobody stays there. An eGo with refillable "clearomizers" like the Kanger EVOD (which became my favorite before I got an advanced widget) is what I'd consider a "starter".
No, you are not at all limited to any one source for liquids. The problem that can crop up with "cig-a-like" units is the cartridge ("cartomizer") that holds the
juice. You have to know, for one, which screw threads the batteries use. The 510 standard is maybe the most common and widely supported. Whichever you use, you can buy empty cartomizers and fill them yourself. Not hard but kinda tedious I think. I switched pretty fast to
tank like systems where refilling is "squirt
juice in" and that's about it.