Hold down the keys connected by a plus sign together. Release and follow by key listed after a comma.
So, for CTRL+SHIFT+&, o or O you would:
Hold down the CTRL Shift and & keys at the same time, then release them and press o or O

Press (Windows)

Press (Mac)

To get this

CTRL+` (ACCENT GRAVE); then type the letter

Option+` (ACCENT GRAVE); then type the letter

à, è, ì, ò, ù, | À, È, Ì, Ò, Ù

CTRL+' (APOSTROPHE); then type the letter

Option+e; then type the letter

á, é, í, ó, ú, ý | Á, É, Í, Ó, Ú, Ý

CTRL+SHIFT+^ (CARET); then type the letter

Option+i; then type the letter

â, ê, î, ô, û | Â, Ê, Î, Ô, Û

CTRL+SHIFT+~ (TILDE); then type the letter

Option+n; then type the letter

ã, ñ, õ | Ã, Ñ, Õ

CTRL+SHIFT+: (COLON); then type the letter

Option+u; then type the letter

ä, ë, ï, ö, ü, ÿ,  | Ä, Ë, Ï, Ö, Ü, Ÿ

CTRL+SHIFT+@, a or A

Option+a or Option+SHIFT+ A

å, Å

CTRL+SHIFT+&, a or A

Option+ ' (Single Quote) or
Option+SHIFT+ ' (Single Quote)

æ, Æ

CTRL+SHIFT+&, o or O

Option + q or Option+SHIFT + q

œ, Œ

CTRL+, (COMMA), c or C

Option + c or Option+SHIFT + C

ç, Ç

CTRL+' (APOSTROPHE), d or D

 

ð, Ð

CTRL+/, o or O

Option+ o or Option +SHIFT + O

ø, Ø

ALT+CTRL+SHIFT+?

Option+SHIFT+?

¿

ALT+CTRL+SHIFT+!

Option+1 (numeral one)

¡

CTRL+SHIFT+&, s

Option+s

ß