You have a couple of easy options!
From the My Studies page, click on the required study.
Click on the App Templates tab.
Each Template will have its own unique QR Code and web link.
You can either save the QR Code as an image (right click and save) and include it in whatever medium you are using to communicate to participants (eg: email to the team, in a brochure to the wider community, social media post).
If you are expecting participants to use their desktops/laptops to participate in the Study, you can click on the green link icon to launch the webapp in a new page. Simply copy and paste this link to your participants.