Ok I would make lotsa things:
1-Place a portal in the toilet and another in my couch or computer chair. Then I could poop and pee whenever I wanted without leaving the screen.
2-Place a portal in my friend’s house and another in my bedroom, hidden. Then I could go to his house whenever I wanted.
3-Place one in my bedroom an another on my school entrance. Then I could wake up just in time and go to school in less than 1 second.
4-Go to some place with a high roof. Place one portal in the roof and another on the floor bellow it. Then i would fall forever and scream “LEROOOY JENKINS!”
5-Place one inside the cinema and another in my house. Then I could go to cinema whenever I wanted, without paying!