Texture paint is grainy in some areas of the mesh and solid in others. I am also not able to select regions for paint masking

Thanks for taking the time to look at my problem. I have never modeled a day in my life but recently I am trying to learn more about Blender as my company produces incredible models and I personally want to learn more about the process. I have created my first model (Gabe) through a guide available on SkillShare. The guy is using the same version of the program I am, but appears to be getting different results.

For instance, some of my paint is turning up "grainy" in some areas and smooth in others such as the feet.

Additionally, there are strange lines on the feet that I cannot paint over.

Lastly, I am unable to select parts of the model/mesh with the masking tool function such as the upper and lower parts of the beak. This is probably something I am not understanding/messing up on as the guy in the tutorials kinda just did it without showing specifically how to do it, just vague steps you can only make out if you are going at 0.25x.

Thank you all so much for the help!