Start your installation on forestadmin.com, by clicking "Install Forest Admin":
You'll be taken to a sign-up form to create your account and first project:
On the next screen, click on "Plug your datasource" to get started:
At this point, you face 2 choices:
Generate a dedicated admin panel application from your database;
Install directly Forest Admin into your existing application if it's one of the following: Rails, Express/Sequelize, Express/Mongoose.
If your application uses a framework we support, you should definitely go with the second solution, because your relationships between tables will be added and updated automatically. Otherwise, Lumber is a great alternative which generates an admin panel application inside your app.
Once you've made up your mind, select your datasource and follow the on-screen instructions: