Another easy question.... (might be that)
What emulator do you use? Fceux? or the one that come with NESMaker?
If the one that come with NESMaker... the key (of the keyboard) to move the player are not the up,down,left,right.... try "esc" key to see what are the controls.
If you prefer, as Joe explains in a video, you can configure NESMaker to use another emulator. For development / debug, "fceux" as recommended by Joe is a perfect solution (download it on internet, unzip, and then you can configure in NESMaker). It's explained in the "NESmaker 0 - (pi beta) The Basics of the Interface" video at 10:00 :
https://youtu.be/D24fxPMKke8?t=10m