The third way to create new instances is via the corresponding overview.
The start link Process App - Overview is normally used to search the overview table of all instances. However, it is possible that the instance you are looking for does not yet exist and you want to create it directly. In that case, you don't have to leave the overview: Each overview form automatically contains a button New (which can be deleted or renamed from the form by a PAS design user).
The button in the overview form opens the corresponding input form directly and allows you to enter data.