This standard license grants you a non-exclusive, non-transferable right to use the icons. To give you a brief idea, you can use your purchased icons in the following ways:
Sure thing. That‘s why you probably purchased them, right?
Yes. Feel free to take the icons as a basis and modify them to your own needs.
No. You are not allowed to integrate the icons into a template or any digital or physical good that is distributed in any way. If you need such a perk, make sure you upgrade to the Extended license.
No. This license avails you from crediting the author. However, if you want to write me a testimonial, I can give you a generous discount voucher for your next purchase at my shop. [Write to me](mailto:firstname.lastname@example.org?subject=Testimonial%20for%20a%20discount%20voucher) if you are cool with that.