If you are interested in hand embroidery there is a series of books put out by Country Bumpkin that give clear instructions along with step by step pictures. A~Z of Embroidery Stitches, A~Z of Wool Embroidery, A~Z of Embroidered Flowers, A~Z of Ribbon Embroidery, A~Z of Bullions, etc. Because I am a visual learner these are my go to sources. In running a google search I found you can now download the books in PDF.
Images for a-z of embroidery stitches pdf