3rd Day Update:
I now have something somewhat resembling a game (yay!). The character now have walking animation as well as jumping animation.
Here's a gif showing how it currently looks:
In addition, codes are also provided below:
Credits to the Godot Platformer Tutorial by BornCG
I'm still testing out if the constants are good enough. In addition, I still have a number of animation (albeit very simple) such as crouching that I have not utilize yet, but this is good enough for now. Will start making maps tomorrow!