I want to apply the GNU GPL 3.0 license to my open source project, but have literally zero experience using any kind of licenses. Would someone mind showing me the way on this? I found the actual license here, and if I understand it correctly, all I have to do is copy and paste that "notice" somewhere in my project? As of right now, I made a .dm file to hold a commented notice and a .txt file with the notice in it in my project. Do I need to do anything else?

Upon reading tldrlegal's summarized version of the license here, I need to also include "install instructions." I threw that into the same 2 files (the .dm and .txt files) how to do tat for anyone outside this community.
A license is basically just a notice that also constitutes a contract, between your and the party using your software and code. As such, you simply need to put it somewhere in your project where a person would be readily expected to see it, or be able to see it. I just put mine in a file called "", the plus sign to make the file appear near the top of the file list.

As for that link, that it's restrictions and requirements on the license holders, i.e. the people downloading, using, modifying, and redistributing your project. As the owner, they do not necessarily apply to you, though you're free to follow them if you wish.
In response to Popisfizzy
So what I've done already is just fine? Excellent. Good to know it isn't really complicated. I thought there was some extra stuff I'd have to do to the project in order to make it comply with the license.