Brush lettering is a form of calligraphy, where you use brush pens to write letters. It's a quite simple technique with two main rules: create thin upstrokes and thick downstrokes by changing the amount of pressure while writing.
Check out our brush lettering and calligraphy books and workbooks. They will help you learn step by step different letter styles that you can then practice on your own. Just remember to make sure that your practice pad has smooth paper, otherwise, you can damage your brush pen.