hi,
new user here. had issue with some of my brushes just coming out as ‘squares.’
You need to select an alpha.
Hey there,
looks like your real problem is that you simply aren’t in edit mode. Clear the canvas (ctrl + n) draw out your model again and this time don’t forget to click the edit button. After that your brush will behave totally different 
Hope that helps.
i know these thanks are late in coming…
but thanks 