The study type is the type of sites you want to include in the study. Only sites with the study type selected here will be able to be allocated to the study in the 'Allocation' tab e.g If you select just 'Hospital' then only Hospitals will be shown in the 'Allocation' tab. The selected types are on the right hand side. To move a study type click on one or more and click the arrow button to move it to the other side.
Click 'Update details' when you have finished to save your settings, the allocation tab will not update until this is done.