Select next occurrence of the current word or selection: ^G (macOS) / Alt+J (Windows/Linux).
Select all occurrences: ⌘⌃G (macOS) / Ctrl+Alt+Shift+J (Windows/Linux).
To add or remove multiple carets, you can also press and hold the ⌘ (macOS) / Alt (Windows/Linux), then click to add a new caret. You can also make a multiple selection by holding Shift+Alt and dragging the caret.
To remove all the carets, press ␛ (macOS) / Escape (Windows/Linux).