First of all you need to open your picture in inkscape. Make sure that your photo is not blurry, not too small, and properly lit so that you can see the features. Inkscape is a vector graphics program, you can read more about it here
. For more about vector graphics in general, you can see it here
. It is important to know that inkscape doesn't work like Paint. For example, you can't just use a paintbrush tool and draw a line. It uses mathematical equations to create simple 'objects' which are geometric. Inkscape also uses paths. I will mention paths quite a lot here, as we use them for most of the picture.