If tabletop roleplaying games were video games, D&D would be Super Mario Brothers. It's the biggest, it's the most universally recognized, and it only scratches the surface of a very rich and diverse form of entertainment. And like Mario's World 1-1, it's still probably the best place to start roleplaying.
Dungeons & Dragons easily introduces the fundamentals of pretend gaming in a beautiful package. One player comes up with a cool dungeon, draws it on a piece of paper (or computer screen), and everyone else plays an adventurer trying to explore it. You fight monsters. You take their treasure. You get stronger and find bigger weapons to help you explore bigger, scarier dungeons. Rinse and repeat until you're the strongest in the land, or until real-life responsibilities stop Sarah from showing up on Thursdays and the whole thing falls apart.
Are there better games out there with friendlier, more streamlined rules? Yeah, probably. Almost everyone has a strongly held opinion of what the perfect beginner game is, but D&D is still the top dog, and may always be the main reference point in the hobby.
The Dungeons & Dragons Starter Set remains the best place to begin. For a reasonable price you've got the game's rules, some beginner characters, and a decent pre-written adventure module that'll keep you and your friends busy for a couple of evenings. It doesn't come with a lot of flashy, distracting bits and bobs ... only the bare minimum to get you playing, and that's a good thing.