In order to become a PhD student at the Department of Chemistry, you must have been hired in a PhD-fellowship position. These are normally openly announced as 3 or 4 years fellowships.
Within 2 months after starting in a PhD-position, you must apply for admittance to the PhD program in Science at the Faculty of Science and Technology (link). For PhD-students at the Department of Chemistry, there are currently two lines of study to choose between in the Science program: PhD in Chemistry or PhD in Molecular and Structural Biology.
The admittance application includes a form and a project description. The form includes among other things a proposed educational component, which consists of 30 ECTS of PhD courses. The application should be worked out jointly between the PhD-fellow and the supervisor(s). Note that the application needs to be approved (and signed) by the Head of Department prior to submission to the Faculty.
Some useful links: