We have two ways you can use autocomplete in the editor: you can enable it as an always-on feature, or you can trigger it with a keyboard command.
You can turn on autocomplete in your editor settings. Check the "Autocomplete" check box, then save your settings by pressing the green "Save All Settings" button.
When autocomplete is enabled this way, you'll see autocomplete suggestions as you type in the HTML, CSS, and JS panels of the editor. You can select autocomplete options with your keyboard arrow keys or by clicking on them.
Autocomplete Keyboard Command
If you'd rather use autocomplete on demand, you can trigger it with the keyboard command
You can select an autocomplete suggestion with your keyboard arrows or click it to add it to your code.