To enable set your price on a simple product, scroll down to the product data section within the edit screen for the selected product.
Toggle on the checkbox highlighted below, this will hide the default pricing and sales fields and they will be replaced by a minimum and suggested price fields.
The minumum price field defaults to 0, enter the cheapest value that customers can enter
This field will autopopulate the Set your price product field to entered amount, and will be displayed as the product price.
Shown below is the output for a Set Your Price product that has a minimum price of 5 and a suggested amount of 10 (please note that text can be changed on the output, please read the labels section of the documentation).