Question

how to ask the user their first name

Answer 1

What language are you after?

In C (and C++), you could do the following:

#include <stdio.h>

int main()
{
    char name[32];                                // We'll have a variable called "name" and can store up to 32 characters.
    printf("What's your name?\n");                // Asking the user for their name.
    printf(": ");                                 // Showing a prompt.
    scanf("%s", name);                            // Reading the name from the standard input.
    printf("Why, nice to meet you, %s!\n", name); // Using the "name" just to verify all went well.
    return 0;                                     // The program terminates indicating no error.
}