Suppose there is a textbox with the field name 'Comments' and you want to show a tooltip on the textbox field whenever a user does a mouse over on that field, you can use the drag and drop code editor to define a condition like below upon the 'onFocus' event:
Here are the steps to understand how you can define such a condition:
From the left panel, click on the 'Custom Functions' option. Select the third block called 'Setter' and drag it to the centre of the editor.
In the 'Control Name', select 'Comments'.
In the next option called 'Property Name', select 'Tooltip'.
In the next option, 'Value', enter the text 'Enter your comments here'.