Use the Clue Editor tab to add clues to your puzzle
To enter clues, you can click on the word in the list of clues or on the grid. When a word is selected, use the text box above the clues (reads "One across clue" above and has a visible cursor) to edit the clues. The text box will not be visible until a clue is selected.
You can also use the tab key to move to the next clue in the puzzle.
Resources
If you need help cluing your puzzle, I would recommend Matt Ginsberg's clue database. You can find the installers here: