The basic guidelines are as follows:
You can use our icons both as main and secondary elements of your designs or products (digital and physical).
You can download our icons of up to 100*100px in the PNG format and use them at no fee for both personal and commercial purposes. If you are using our icons for free, please provide a link to our website. For details about linking, click here.
If you need a wider choice of icons, formats, and sizes, — or don’t feel like adding links to Icons8, — consider subscribing to one of our paid plans.
If you want to integrate your app or service with our assets to let your users use them in their projects, you will need to subscribe to one of our API plans.
If you want to use icons in your templates, please see this article.
It is prohibited to redistribute or resell icons. There shouldn't be any way to access and download the original files from your project.