The int type stores whole numbers like -5, 0, 42, or 1000. You cannot store decimals in an int. If you try, C++ discards everything after the decimal point. An int typically uses 4 bytes (32 bits) of memory.
This is enough for most counters, indices, and calculations that stay under 2 billion. Example: int age = 25; stores the number 25. You can then use age in calculations like age + 1 or age * 2 to compute new values.