IT typically deals with computer based infrastructure solutions.
Making sure everyone has the proper image on there computer can access all necessary resource such programs or networked drive...ect.
Setting up company wide email or some other system
You could sum it up as the study of commercial computer systems and their deployment.
Computer Science is just that, a science involving the study of computer based algorithms. For example, operating system design, compiler design, programing language design, or some more typical algorithmic transformations such as sorting algorithms, image transformation. and audio processing.
For completeness, CS is not Software Engineering. Although many CS majors end up as software engineers, the disciplines are very different yet often complimentary. For example, a CS professional might developed an echo cancellation algorithm. Then a software engineer figures out how to integrate that algorithm to a telephone system with multiple TDM buses and channels. I believe the main difference between science and engineering in general is the difference between theory and practical application.