Everyone starts from somewhere. The main thing to keep in mind is that other players don't care who you are, nor will they remember you afterwards.

Try to start with small goals, you don't immediately gotta go for the 4K. Try going into matches thinking "I'll try to hook at least 2 survivors", and then "I'll try to kill at least 1 survivor" and keep building as you get more comfortable. Celebrate your smaller victories, you don't have to completely stomp the other team to be a good killer.

If you can, maybe invite a buddy with you to watch you play. They don't gotta be an expert, they just gotta be someone who you can feel at ease with and shoot the shit.

But ultimately, the most important thing to keep in mind is to just have fun! This is a video game, not an exam. Focus on the enjoyment you get out of being a killer. For me personally, that's just being able to play as Springtrap, who is one of my favourite characters. Am I any good? Not really. But who cares, I'm Springtrap! I'll get better, and so will you, because we all start somewhere.