First, you don't need malloc in programs written by beginners.
Modern computers won't even flinch at an array like char s[1000000];.
Also, in embedded systems, it's the opposite—malloc should be avoided as well, for memory conservation.
Taking that into consideration, please read the following usage.

Allocate memory as follows:It's the same for data types other than int.even with structs.
int *data;
data = malloc(sizeof(int) * required_number_of_elements);

The allocated memory can be used just like a regular array.
data[i] = 10;

If you want to increase the number of elements, do it like this.
data = realloc(data, sizeof(int) * required_element_count);

If you no longer use the array, free it like this.
free(p);

However, if the program is very small, it's not necessary to deallocate memory using the free function.
Forgetting to release resources in large programs can lead to what's known as a memory leak, where memory usage gradually increases over time.
Therefore, to cultivate the habit of releasing resources, always call the free function.