Acute

Option + e then letter = letter with an acute accent
Example - option + e then a = á

Grave

Option + ` then letter = letter with grave accent
Example - option + ` then a = à

Tilde

Option + n then letter = letter with a tilde
Example - option + n then n = ñ

Umlaut

Option + u then letter = letter with an umlaut
Example - option + i then u = ü

Circumflex

Option + i then letter = letter with circumflex
Example - option + i then a = â

Image credit: Audience at Club Red Radio, 2000 Native American Film and Video Festival - photograph by Amalia Córdova, NMAI