first off id like to say that I’m brand new to blender and 3d animation in general. i have done some basic cad software in engineering. i started off as my first project trying to make a basic figure. now i am having trouble rotating the figures legs to make his fee flat, but not change the angle of his legs. any tips…thank you 
Mesh / Transform / Shear menu. Then press either X or Y to change the shear axis, then drag mouse
or
Scale along the Z axis by zero = S Z 0