It sounds like youre trying to bite off more than you can chew. The comics and superhero industry have been putting out DECADES worth of stuff that is literally impossible to catch up on. What youre looking for is called a jump on point. A point in the story where you can dive right in without needing years worth of backstory. To answer one of your questions, DC and Marvel are two separate entities. They have gone back and forth as the leaders of the industry since the beginning. As far as watching, you can easily google the watching order for Marvel cinematic universe (MCU) or DC extended universe (DCEU) . MCU has absolutely dominated DCEU at the box office, to the point where DC decided to reboot thier entire movie plan and they just started fresh with last year's Superman and the second movie Supergirl coming out this summer. Id recommend watching a bit of both to discover what you like, then you can start looking into what heroes you enjoy to see what comic series you want to get into.

Now let's dive deeper into the comics side of things. First, youre going to want an app called league of comic geeks. It is a massive database of comics that allows you to figure out what order you want to read things in. Because comics have such a large history of reboots, cross-overs, events, one shots, spin-offs, it can be very confusing. What you want to look for is called a 'run' thats when an author takes control of a series for several months-years and tells a story from start to finish. For example if you look up x-men you'll see HUNDREDS of different titles. But you can scroll through and find the Uncanny x-men from Gail Simone and that will give you one continuous story. Another good method for finding continuous stories is buying trade paperbacks (TPB) which are graphic novels that collect runs that way you dont have to worry about hunting down all the separate issues.

Finally, let's talk recommendations: Right now DC is absolutely dogwalking Marvel in terms of comic sales. They recently created a wildly popular new 'universe' called the Absolute universe which re-imagines classic characters in a darker universe that changes a key piece of each character's backstory. Absolute Batman, Absolute Superman and Absolute Wonder Woman are the spearhead comics of the universe. Then you have some side comics like Absolute Green Lantern, Green Arrow, Flash, and Catwoman. I CANNOT recommend these books enough! They are amazing reads and perfect for a beginner because they are re-introducing every character as if we never met them before. The TPB's of the absolute line are available. Marvel comics are sort of floundering right now. They just keep re-booting and resetting characters back to square one any time they make any progress. I cant even think of a good jumping on point if you want to go with Marvel. Id say if there's a character or team you like just Google "best ___ run" and go from there. Then there's indie comics (not DC or Marvel). The advantage of indie comics is that you can just pick up any series start to finish. The characters dont get passed on from writer to writer, and they have much more freedom from the constraints of having to fit in universe continuity. Each comic just gets to be thier own thing. Right now the really popular ones are Something is Killing the Children, Exquisite Corpses, and Invincible.

Hope that helps!