I don't disagree with lucebruce's statement that "not everyone needs to be good at fighting games" but I think there's an implied second part of that statement could read more like "not everyone needs to be good at fighting games, but if you want to learn one, pretty much anybody can become a decent player."
If you just started playing SFIV recently, it's going to be very difficult to win online for a while because the game has been around for 8(ish) years now, so at this stage of the game, most people online are going to at least be competent. It's a pretty different experience than if someone decides to get into something like Overwatch. In both the SFIV and Overwatch scenarios, you'll be bad at first, but there are some key differences that make a game like Overwatch more approachable:
1) It's a team-based game, so you can still get carried to victory even early in the learning process, and getting wins is obviously encouraging.
2) The player base is huge, so it's much easier for the online matchmaking system to find you similarly skilled opponents to play against.
3) It's a team-based game, so you can take solace in your individual performance being good (even if it may not be) in the face of a loss.
4) It's in a genre where single-player modes are somewhat better at teaching you the fundamentals of the genre, and it's a generally popular genre, so many (most?) players are coming in with some fundamental skills, at the very least.
5) It's a team-based game, so you can play on the same team as real life friends and they can explain things to you as they happen in voice chat or whatever.
6) It's a team-based game, so you can blame others when you lose and don't have to take any personal responsibility for the team's performance, but when you win, there's a natural tendency to credit your personal contribution.
I think it's really important to realize that a lot of the time when people say "fighting games are impenetrable" they actually should be saying "1-on-1 competitive games are significantly harder to get into than team-based games." I think fighting games get stuck with their image because they're a lot of people's first time really trying out a competitive online 1v1 game. If 1v1 arena shooters were a huge genre, I think people would say exactly the same things about them that they say about fighters.
If the absolute basics of fighting games are something you want to learn, I would recommend watching something like
Sirlin's beginner Street Fighter II videos, as they are pretty great for wrapping you head around the basics of the genre.