Since you were using very short range weapons from what the picture shows, I recommend switching to a mid range shooter to see how it suits you. For people learning the game, I would highly recommend the Tentatek Splattershot, which unlocks very early, and has a great kit to it. For that kind of weapon, it's important to keep your distance, and keep moving when battling someone else. And if they out range you, retreat and try to get the drop on them later, or use your sub to intimidate or trap them and get up close, it depends on the situation.
And if the Tentatek does not sit well with you, just try out a whole lot of weapons, even if you are not good with them initially, practice makes perfect. Also, when learning a new weapon, go to the practice range to get a good understanding of how the weapon, its sub, and special work. Going into battle knowing all that will make a huge difference.
If you aren't already, I highly recommend using the motion controls for aiming. Especially if you start practicing longer range weapons. They feel very weird at first (I even spent most of my playing Splatoon 1 using sticks because of that) but getting used to the motion controls will be vital advantage in the long run. And if want to practice the motion easily, play the Single player with it, you should get the hang of it doing so.
When using specials, don't be afraid to use them, but don't rush doing so either. For example, the ink armor should only be used when you know your team is all alive, or if you can see a few of your teammates in the distance approaching enemies, that will make a huge difference. It's important to know what each special does, so try each out in the practice range to get a feel for them.
Finally, just keep on playing. I get it can be frustrating to play the game, knowing there are a lot of vets from Splatoon 1 running around who know how to play. But if you keep playing the game and practicing you will get better. Pay attention to what your teammates and enemies are doing. If at the end of the match you see they are on top of the team with a good amount of splats, hope that they stay in your lobby so you can observe them as an enemy or ally.
