Advanced vehicle Blueprints

So I am very bad at using unreal because I don’t know what I’m doing. Then when I look things up I can’t find any tutorials that work for me.
I’m making a game with some friends for a project and I’ve been wanting to assign the left shift key the ability to add a speed boost to my vehicle. On top of that I also wanted to make it a split screen multiplayer game and I have only found tutorials for split screen FPS, none of it is working.
If you have a solution please do not spare any detail, I need ALL the help I can get.