Get Visual Studio 2017 Community, Sourcetree (Git user interface) and the source code from Valve's Github.
Visual Studio 2017:
https://www.visualstudio.com/downloads/Sourcetree:
https://www.sourcetreeapp.com/Source code:
https://github.com/ValveSoftware/halflifeThis documentation explains where to get the address used to clone Git repositories:
https://help.github.com/articles/which-remote-url-should-i-use/Here's a Sourcetree tutorial:
https://confluence.atlassian.com/sourcetreekb/clone-a-repository-into-sourcetree-780870050.htmlTake the HTTPS URL from Valve's Half-Life repository and clone it using Sourcetree, then you can open the project file projects.lsn located in "projects/vs2010". This contains the client and server libraries for Half-Life, Ricochet and DeathMatch Classic. You may remove the latter 2 if you don't want them.
After that it's basically the same as any other C++ project, but you should make sure you understand the basics of the language first, then read tutorials about Half-Life programming.
Here's a good C++ tutorial:
http://www.cplusplus.com/doc/tutorial/Here are some Half-Life tutorials:
http://twhl.info/tutorial.php?cat=1This looks like a lot of work, so take it slow and one at a time. Get Visual Studio installed and follow tutorials for C++ first so you understand it.
You will likely have issues with it, everybody does at first. It's not an easy language to learn but the most important thing is to keep at it. If you don't understand something, just ask.
If you need help with C++ in particular you can ask for help here:
https://www.reddit.com/r/cpp_questions/https://stackoverflow.com/If you don't have much experience using Google you should try to use it to find answers first. Prefix your searches with "C++" to narrow it down.
Unfortunately there is no easier way to mod Half-Life. Some of us are working to make things easier. What you're trying to do should be possible with HLEnhanced eventually, but it's not ready yet.
If you don't want to learn how to program or can't, one of us can provide you with the necessary changes. It doesn't sound like a lot of work, but i do recommend learning to program if you want to do more advanced modding later on.