Need Help with Simple Player Controller On side Scroller

I’v been working on a small project where you control a rocket, and i have been having a hard time with getting some sort of acceleration going, i have tried creating my own float values, and using the player acceleration, but at most all it does is slow my character down when walking left or right, if i put in my own value add force block it works just fine but it is instantaneous, and after many methods i can figure anything out and need a little help, mostly probably with what i am doing wrong, in the end id like the player to press a key to accelerate and use other keys to change direction. then i can go about setting up fuel and other things