All of this information is detailed in the license file for Construct 2: https://www.scirra.com/store/licensing#license2
But basically, for the free edition, these are the rules:
The Free Edition is permitted for use by anyone for non-commercial use. Commercial use counts as but is not limited to: use within any business (other than limited testing for suitability), generating advertising revenue, selling or licensing generated content or intention or capability to generate revenue.