If you don't have a Spanish keyboard on your computer your main option is to switch autocorrect to detect the Spanish language that way if you write a word that needs a Spanish letter that English doesn't have autocorrect will change it for you and add the correct letter. You can also go into the special characters section in google doc or microsoft word and it contains Spanish letters you just need to find them. If you're on a mobile device usually you just need to add a Spanish keyboard in your settings
