a source mod uses games like portal and lets the creator of the mod customize it as much as he/she wants to. this has even greater power than the console(link to a guide about this can be found here) because you can do things like change the title of the game.

navigate to this directory C:\Program Files (x86)\Steam\steamapps\common\Portal this directory may be in this folder called program files instead but this is the directory I use. now copy the folder called portal (not Portal portal) and go to C:\Program Files (x86)\Steam\steamapps\sourcemods then paste the folder you just copy'ed in there. now rename the folder to the name of your mod but make sure there are no spaces in the name of the folder. you should now have your mod set up now go into it and remove the steam.inf file. now restart steam and your mod should be there.

go int your mod folder and open up the text file called gameinfo.txt open it it should look something like this:

now you should see two things Game and Title, spaced out is the name of the game, Portal, now select it and rename it but make sure its in quotes. do the same thing with the other part of text that says Portal and now you have renamed your mod.

so you may notice that your when you play your mod the chapters are named yourmodname-chapter1-title# and so on. well lets change this. go into your mod and go to the resources folder and open it, it should look like this:

now you want to rename all the "portal_chapter_(chapter number)_title" with "(your mod folder name here)_chapter_(chapter number)_title" if you are confused then click on the image of the file above to zoom in on it. now lets rename the chapters you should notice the chapter names from Portal like testchamber00 in quotes replace those names with the name of your chapter(s).

I am still trying to figure out a few things on modding thanks for viewing my guide. have a nice day :-)