How to build the changes made in the Open Source project(GNOME)?

I'm interested in starting my journey in open source contribution and would like to know how to make changes to existing open source projects and build them locally to verify the changes I've made on my system.

Specifically, I'd like to learn about the build process and how to verify changes such as tweaking UI elements, enhancing user commands, or adding new tools to an open source project.

Any advice, tips, or resources on this topic would be greatly appreciated. I am a newbie in this journey so any leads will really help me a lot to start the open source contribution journey.

Thank you!