Q: How do I add curved text to a Canva Design?
A: The simple way:
0] select the text box
1] click the “Effects” button in the toolbar at the top of the screen
2] select “Curve” from the left-hand “Effects” palette
3] customize how many degrees the text should cover using the “Curve” slider

The fancy way: install TypeCraft. It gives you more customizable control over text options, but strikes me as overkill 80% of the time.