Windows: use Alt codes with the numeric keypad
Windows: use the Character Map app
Mac: hold the letter key to see accent options
Mac: use Option plus a key, then the letter
iPhone/iPad: press and hold a letter to choose an accent
Android: press and hold a letter to choose an accent
Word/Google Docs: use Insert > Special characters
Copy and paste the accented character from a character table
Use a keyboard layout for the target language
Use Unicode input if your system supports it