Push is released under a Creative Commons — Attribution 4.0 International — CC BY 4.0) license. That means you are free to copy and redistribute the material in any medium or format; remix, transform and build upon the material for any purpose, even commercially, as long as you give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
That being said, you can't use this system to make games that promote bigotry, racism, ableism, sexism, homophobia, fascism, or any other form of prejudiced or oppressive behavior. This is a strict prohibition by the author.
In order to give proper credit, just copy and paste the text below into the credits of your game:
This work is based on the Push SRD, developed, authored, and edited by Cezar Capacle (https://capacle.itch.io/), and licensed for our use under the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0/).
If you want to, you can use the Push-powered logo in your games, available as a separate file with this SRD.
This game is accompanied by the following templates:
For all purposes, the templates are a part of this SRD and follow the same license.