Introduction to Computer Science from Harvard University is a free course that covers the basics of computer science. The course is designed for people with no prior experience in computer science, but it still contains valuable information for those who want to refresh their knowledge.
The course is divided into two parts: Data Structures and Algorithms. In the first part, you will learn how to store and organize data efficiently in a computer system. You will also learn about the fundamental data types and how to work with them. In the second part, you will learn about algorithms and how they are used to solve problems that involve processing data. You will also learn about SQL and Python programming languages which are used by most programmers today.