To type lowercase letters with accent marks, simply press the Ctrl key, and at the same time press the apostrophe/quotation mark key. Then press a, e, i, o, or u. For capital letters with accent marks use the same method. Only press the Caps Lock key beforehand. This Ctrl + apostrophe method may not work in some applications or with some hardware. I am not sure which ones.
In Windows the combination of the ALT key and certain numerical codes produce non-English language characters. Those we use for Spanish language and their codes are listed below for your convenience.
CAPITAL letters w/ accents: lowercase letters w/ accents: Punctuation marks for Spanish:
Á Alt key + 0193 á Alt key + 0225 ¿ Alt key + 0191 (inverted question mark)
É Alt key + 0201 é Alt key + 0233 ¡ Alt key + 0161 (inverted exclamation point)
Í Alt key + 0205 í Alt key + 0237
Ó Alt key + 0211 ó Alt key + 0243
Ú Alt key + 0218 ú Alt key + 0250
Ñ Alt key + 0209 ñ Alt key + 0241