IGCSE Computer Science teaches how a computer works and how problems are turned into algorithms.
Two sides
The first is theory: number systems, data representation, hardware, networks, security and software.
The second is algorithms and programming: problem solving, pseudocode, flowcharts, code tracing and debugging.
The exam format surprises people
The course teaches programming and the exam is mostly taken on paper. The student is asked to write pseudocode or a flowchart, not code that runs on a machine.
That is a separate skill. A student who writes code comfortably at a keyboard can lose marks for not knowing the expected pseudocode conventions.
Code tracing
Writing into a table, step by step, what a given piece of code does. It is the part of the exam that most rewards practice and improves markedly with regular work.
Speed matters here: writing every step takes time, and a rushed trace table is usually wrong.
Which language
The course does not impose a language; schools generally use Python or something similar. Where code is required a language may be chosen, but the pseudocode conventions are learned separately.
The difference from ICT
ICT teaches using ready made tools; Computer Science teaches understanding the system and building algorithms. For a student with a computer science target, Computer Science is the right course.
What follows
It is a strong bridge to A-Level Computer Science and IB Computer Science. It also overlaps conceptually with AP Computer Science A, with a difference of language.