I don't know what keyboard layout you use, but if you're working with qwerty.
You can set up your input language to be US international.

With US-international you hold down alt-gr to do most modifications. (alt-gr is the right alt key)

While you can do that for most keys, I find it easier to remember the accent combos. Such as apostrophe-a creates á and so on. alt-gr+n becomes ñ and alt-gr+/ becomes ¿

Since the method of setup is vastly different between windows 8 and prior versions of windows. And I can't speak for the Macintosh keyboard since it is actually quite different from the windows keyboard. I'd probably need more information to be able to help you set it up.

Since you probably don't have a language bar on your computer. Mine has a language bar because I sometimes type in Japanese, and in case I ever want to accent words, my default layout is US-international.

Thank you. I'm using Querty on windows 7.
Never used a Mac but I understood enough to search for the language bar which was already set to United States-International. Although I didn't know how to use it.
Found a table:
'(APOSTROPHE) - c, e, y, u, i, o, a = ç, é, ý, ú, í, ó, á
"(QUOTATION MARK) - e, y, u, i, o, a = ë, ÿ, ü, ï, ö, ä
`(ACCENT GRAVE)- e, u, i, o, a=è, ù, ì, ò, à
~(TILDE)- o, n, a = õ, ñ, ã
^(CARET)- e, u, i, o, a = ê, û, î, ô, â

By the way I realized why I get so many error with ' and ".

Still missing how to type fast the ¿ and ¡

I didn't mention the entire table for the fact that I thought you'd catch onto the pattern quite quickly.
With practice with alt-gr you can learn many shortcuts. For instance I find it a lot more natural to alt-gr+n to create the ñ character than to actually use the tilde. Of course for characters such as ã and õ you'll sometimes have to type it the long way.
Oh yeah I forgot to mention alt-gr+1 is ¡ That's an important character in Spanish as far as I'm aware.

In order alt-gr+/ is ¿ and alt-gr+1 is ¡.