To view the My Subjects tab you do require the Teacher role on ScholarPack, so if you can't see this tab, you do not have this role.
If you have the Admin tab you are able to enter summative assessment via Admin > Students > Assessment Checkpoints (pink flag) or alternatively if you speak to the SysAdmin or Admin in your school they will be able to allocate you the Teacher role.
If once allocated you cannot view any classes here you may need to be assigned to the classes you require via Admin > Classes > Add Teachers to Class.