Character Feels Slow and Non-Responsive

I recently started game development, I am using Unity ( JavaScript ). I would like to make my first game something simple like Geometry Dash ( Obviously not as good art and stuff ). My character is a cube but feels very sluggish and sometime the "space" to jump doesn't work. I was wondering if there is a way to stop the jump feeling like it's floating and just make it feel like it goes up and comes down. If that makes sense. Oh and the game is 2D. I am not very good at coding and am very new. So any help would be greatly appreciated, cheers.