There is an example of a platformer shipped with Construct 2 called "Example: Physics - rolling platformer." Open Construct 2 and create a new project. From the template selection, scroll down until you find the above template name and select it. By following the example template, you should be able to get what you need.
You could find this information by reading in the tutorials about physics. Take a look at the tutorial linked below:
https://www.scirra.com/tutorials/64/phy ... the-basics
I hope that gets you what you need and good luck with your project.