If you click on the pink bit of the thread you have created you can see all the answers. Immediately underneath the original question is a white box and it has "Answer now" in red at the bottom right hand corner. You type your answer in the white box and then click on answer now. That adds an answer to the original thread rather than creating a new one.
You can reply on your own thread in the "your answer" box.
Giving crossword clues, you can ask a few on the same thread-and say if it's cryptic or if there's a theme (for a quiz). put the whole clue as it's written. One clue on each line with the letter count.