Word completion assists you to input words faster, such as when typing reserved words of programming languages, by typing just a few letters and selecting the complete word from the candidate list.
To complete a word, follow the instructions below:
Type the first few letters of a word.
Choose the Complete command in the Edit menu, or press either Option-Esc or F5.
Choose the word you want to input from the list.
To close the list, press Esc.
Under the Completion section in the Edit settings pane, you can change the types of possible completions that appear in the list. For example, the list can include only the words in your document, or the words specified by your syntax additionally.