tools

blender

pribambase

https://www.mixamo.com

characters

It's usually easiest to have a "character turnaround". Having a front and side view is all you need.

You can drop the image or images into blender. Then, to remove any rotation and movement you can use alt-r and alt-g respectively. Then scale it up, and rotate it 90 degrees along the x axis: rx90. Then in front-ortho (numpad 1) you can move your reference image into place and then in sideview (numpad 3) you can move it back a bit to give room to work.

Duplicate it with shift-d and then rz90 to rotate it 90 on the z axis. Move it into place and you're ready to start modeling!