Brace for a wall of text:
Try going through Octo Canyon to get used to some of the Hero weapons (try to use the same sub as that weapon’s kit). That way you can experience a bunch of weapon types without having to pay for them. Pick one you like the feel of, buy it, and take it into Turf War to get the hang of it.
In Turf War, you want to test out its range (both effective [when it can reliably splat] and actual [when its bullets can deal damage at all]), weaknesses, any ways you can get around the weaknesses, and finally, what the main goal of the weapon is, and how you can accomplish it.
Take the Hero/Splat Charger, for example. Its effective range is longer than most other weapons, but it has a weakness to weapons with a longer range, and those that can kill at close range.
To deal with longer-ranged weapons, you can use the Stingray to hit them from behind walls; or you can store a charge and swim closer to hit them; or you can wait for them to fire, and use your superior charge rate to splat them before they can charge. For close-range weapons, you can throw bombs to stop them following you; snipe them before they can get close; stay on high ledges; always have an escape route ready; and attack with uncharged shots or superjump away when cornered.
Finally, the goal of the Charger is to control a wide area including the objective (for Turf War, the centre of the map), stay safe behind the rest of the team, and act as support and a superjump beacon. To do this, you need to snipe opponents, throw Splat Bombs and use Stingray to reveal enemies to your team; and stay alive as long as possible by changing positions often and peaking from behind walls.
Once you’ve figured put how the weapon works, you can take it into Ranked. Figure out quickly whether the weapon’s good for the current rotation - if not, it’s probably better to try again later and turn to a different weapon for the time being, keeping your rank intact.
Otherwise, it’s mostly practice from this point on, so keep at it and try to learn what you’re doing wrong instead of giving up - none of the Hero weapons are bad (some are better for Turf War though, try their alternate kits in that case), so if you keep dying there’s almost certainly a way to fix that.
Tl;dr: I don’t care, read it anyway you jerk.