There are two options. Go to tables.
First option:
Choose wizards and drag author button to wizards column. Press on green + and save the new field in your table.
Second option:
Choose data types on the left side of your screen. Drag "Joomla user" and drop it into "Data fields". Save new field.
Your table field is created.
Go to pages, choose view, click on "fields", click on + next to your joomla user field name and drag and drop right of the user entry to your grid, fly or form (depending on view).
