Looking to buy a used car Toronto - need help

Hi!

I am trying to buy a car for the first time . I’m on a budget so looking for cheap (under 6k) and used but I have no idea what to look for . I don’t have anyone that can come with me so want to be prepared when I go . I know you should look for under 150k km ideally but what else ?

Also if anyone had good experience with a dealership anywhere in Toronto or Scarborough area - let me know!

Thank you in advance !