Commissioning an artwork is a relatively straightforward process
Contact by whatever way is easiest for you, direct meeting, e-mail, social media.
For portraits say what kind of work you have in mind: a drawing, watercolour, acrylics, oils, pastel, mixed media. Also what style you prefer such as contemporary, traditional, semi-abstract or similar to a famous painting.
I can work from your image source such as a photographic print or digital image that you have and like. I can pick out elements from multiple images to focus on what you want. Sometimes a good quality clear image is not available but you may have a group of images that can be used as references.
The portrait below was created from two reference photos that provided sufficient data to enable me to complete the portrait