hi sir i know c and c++ but i don know how to make softwares , i know about softwares models and all i can make progrnms as well but i want to know how can i make those program interact with my OS ,for example an antivirus software

Most people use C++ as base. Meaning that, they use some type of library that can handle the graphics, and use C++ to code the logic. Every time you make a project, you are making software. For example, when you make a program that checks if the string is a palindrome, you are making a palindrome checking software.