bilingual keyboard

For ñ, hold down the option key, type the "n" key and then type "n"

For ¿, just hold down both the option and shift keys and then type "?"

PS: I'm not familiar with Spanish, only French. But there are many other keyboard shortcuts like this. You can use the "Show Keyboard Viewer" option in the Keyboard preferences menu to see all the possible combinations when holding down option and shift.

The English keyboard can easily make all the characters needed for common W. European languages

Enter characters with accent marks on Mac - Apple Support

For the various accents type and hold down the key you want to add an accent to. The accent menu will appear above the letter and you can either hit the number key representing the accent you want or click on it with the cursor: