My school doesn't use any of these apps

That's completely normal – primary schools especially often have no portal at all. You're not missing out: you can enter tests and dates yourself in two taps, and the timetable lives in patchio anyway.

Entering dates yourself

In the Dates tab, tap “Add date”, choose the subject and type (in your region's wording), set the date, and you're done. The date lands automatically in the family calendar, so everyone knows. A title is possible, but not necessary.

Just forward school letters

Your family has its own email address. Forward the school letter with the date (school outing (Wandertag), parents' evening (Elternabend), test) straight to it – patchio reads out the date and time and suggests the event to you. All you do is confirm it.

You set up the family email address under Manage → Family; how exactly, is covered in the help topic on the family email address. From the “Get dates” assistant, the path “None of these” takes you straight there.