As with so many skills, you get better at it by doing it often. Therefore, identify moments when you can apply this technique -- for example, when you're taking notes, trying to understand something, or trying to solve a problem -- and try it out.
For digital mind maps, Coggle is a handy online tool with the option to collaborate.
Do you feel a bit uncomfortable with color and pictures? A practical mind map without all this still has advantages over linear lists. But do give it a try and compare your black and white version with the colorful version.
Besides mind maps, there are also concept maps. With concept maps you can have several central themes and multiple relationships between the concepts can also be indicated. This extra freedom is sometimes very useful, such as when mapping complex situations. However, it comes at the expense of some focus.
Also use mind maps when studying. Making these kinds of overviews with associations helps you understand and remember.