CPP means c plus plus, better known as C++.
If you want to modify them you need to learn the C++ programming language and know how to use compiler and linker.
However, you do not need this to change spells. Spells are defined in the database table spells_new. You need to learn SQL and you need a database GUI like HeidiSQL. For more Information look here
https://eqemu.gitbook.io/server/categories/spells and here
https://eqemu.gitbook.io/database-sc...lls/spells_new