Verb conjugation of "stützen" in German

My brother moved there last year. He met a woman and went after her. After six years they have broken up, but he no longer wanted to return, because he has settled down in his new home. I am visiting him once a year.
We can help each other with these language studies, this is also the main purpose of Vocabulix. I have already got in touch with some other users. I can speak Italian, but my grammar is weak.
Why did you sit on the box? You obviously did not know that there were presents inside. Now, seriously, do you have a backup plan? We must buy new gifts if we want to go to the party.?