Writing the question
The Question tool is the first one in the tool bar down the left of the screen. Its settings appear in the bar along the bottom, which is where every tool's settings appear.
Type the question, then choose Start the activity. That is the moment the link and the QR code come into existence — before it, there is nothing for a pupil to join.
How many words
One word only
Each pupil sends a single word. This produces the clearest cloud and is right for most questions.
Several words
Each pupil gets up to the number of boxes you choose, between two and ten. They may leave boxes empty.
Let a pupil replace their answer
When this is on, a pupil can change their mind. Their new answer replaces the old one.
Changing the question afterwards
You can correct the wording after the activity has started. Pupils who have not yet opened the link see the new wording straight away; those already on the page keep the version they were given until they reload.
Answers already sent are not affected. If the change is large enough that earlier answers no longer make sense, it is usually better to finish the activity and start a new one.
Tips
Ask for a word, not a sentence. "One word for how you feel about the ending" gives a cloud; "What did you think of the ending?" gives paragraphs.
Several words suits brainstorming; one word suits a check on understanding.