The first page is mostly about you, your home university and the receiving university. You will get the contact information for the guest university after your nomination. If you do not know the ISCED code for your field of studies, then you can research it with this tool.
Before the mobility: All the information for the left column is in the curriculum of your receiving institution. The information for the right column is in the curriculum of your home university.
During the mobility: If something changes during the mobility and you delete a course or add another one, you write it in the left column. Then you add the corresponding courses at your home university to the right column. Make sure that you hit the minimum number of ECTS.
After the mobility: In this table you list all the classes and add the grades that you have received. If the grading system at the receiving institution is different from your own (e.g. A to F instead of 1 to 5), you need to transform them.