C++ is an old but evolving language. In programming, you can use it for almost anything and will find its application in many places. In fact, C++’s inventor, Bjarne Stroustrup, described it as the invisible foundation of everything. Sometimes, C++ might be present deep inside a library of another language because it can be used for performance-critical paths. Furthermore, it can run in small, embedded systems, or it can power video games. Even your browser might be using the language. C++ is almost everywhere.
The language is compiled and targeted at specific architectures such as a PC, mainframe, embedded devices, bespoke hardware, or anything else you can think of. If you need your code to run on different types of machines, you need to recompile it. This has pros and cons. Different configurations give you more to maintain, but compiling to a specific architecture gets you down to the metal, allowing the speed advantage. Whatever platform you target, you will need a compiler. You will also need an editor or integrated development environment (IDE) to write code in C++.