You would fill out the attached form, scan it, and submit it to us via our contact page.
To have a good result it is important that you fill in the form(s) carefully, trying to follow the tips listed in the creation tips article. To get variation in the characters it's best to fill out multiple forms (up to five). The first two are free. It makes sense to start with one and see how you like the result.
Alternatively, we can help you choose one of our existing fonts which approximates your look. That is the easiest and often best route since our fonts are generally well-tested.