Summarize:

You can use easy keyboard shortcuts to quickly insert Spanish accented characters and symbols into any Mac application. You'll use a keyboard shortcut that combines the ⌥ Option key with a character, followed by the character that receives the accent. Here are the different codes for each letter with an accent:   Á or á: ⌥ Option+e, and then type A or a.  É or é: {⌥ Option+e then type E or e.  Í or í: ⌥ Option+e, then type I or I .  Ó or ó: ⌥ Option+o, then type O or o.  Ú or ú: ⌥ Option+u, then type U or u.  Ü or ü: ⌥ Option+u, then type U or u.  Ñ or ñ: ⌥ Option+n, then type N or n.  ¿: ⌥ Option+⇧ Shift+?.  ¡: ⌥ Option+1.
Open the app you want to type in. Find the keyboard combination for the character you want to type.