Before you can take entries to your fair, you must designate the dates for the entry registration period. To enter those, start on the Hierarchy menu, and select the Fair. Then on the Entry Settings tab, the first options are Registration Opens and Registration Closes. Change BOTH of those to be the current year. Save after each. (Opening dates begin at midnight CST at the BEGINNING of the date entered, and Closing dates end at midnight CST at the END of the date entered.)
Your fair may have entry registration dates set differently for some departments. To set different dates, use the Hierarchy menu to select the department, then override the Fair settings with a new date, and Save.