How to Spell-Check Email Messages in Gmail

From the Gooru:

Gmail has your back on spell-check. Gmail has two forms of spell-check to make sure your email messages are free of grammar mistakes and misspellings. You know those red lines that appear under your text when a word is misspelled? That is the automatic spell-check in Gmail. The second type of spell-check is more thorough and catches more mistakes, such as proper nouns that need to be capitalized, or more complicated misspellings.

Read more and see a demo here.