If you're inputting symbols you've never heard of before, you're probably using an international keyboard that inputs them through either Alt Gr key or Compose key. Possible causes for the keyboard or layout misbehaving:
1. You poured tea on your keyboard (or somebody else did). Try a different keyboard and/or wait a few days.
2. A key is stuck: The operating system is thinking that a modifier key (Shift, Alt, Alt Gr, Ctrl) on your keyboard is pressed, either because of a bug or because of some accessibility feature. Try pressing all those keys and/or rebooting.
3. You've accidentally switched to a layout with dead keys by default. Try pressing the malfunctioning keys twice, or try using Alt Gr+Key. If you don't have Alt Gr, try right Alt.