The @ sign has swapped places with the " sign on my Macbook Pro keyboard
Go to the Apple Menu (top left of your screen)
Click on "System Preferences"
Click on "Keyboard"
Choose "Input Sources"
Click on the "+" icon
Select layout name eg. British, US, or ABC  (NOT British PC, which has @ in the wrong place).
Click "Add"
Drag the desired input to the top of the list (drag and drop)


these steps may vary slightly depending on macOS version you have. Should it not be the same please tell us what macOS you have (eg. 10.13 or Mavericks...)