In most cases you (a little inaccurately) call gcc the compiler. A reason is that you can run the whole tool chain, at least for simple projects, with a single gcc command. Let's say you have this main.c

// main.c
#include <stdio.h>
int main(void)
{
    printf("Hello, world!\n");
}

and compile it with

gcc main.c

Then everything you mentioned, cpp, cc1, as and ld will be involved in creating the executable a.out. Well, almost. cpp is old and newer versions of the compiler has the preprocessor integrated.

If you want to see the output of the preprocessor, use gcc -E main.c

As I mentioned, the preprocessor and the compiler is integrated nowadays, so you cannot really run cc1 without the preprocessor. But you can generate an assembly file with gcc -S main.c and this will produce main.s. You can assemble that to an object file with gcc -c main.s which will produce main.o and then you can link it with gcc main.o to produce your final a.out

https://renenyffenegger.ch/notes/development/languages/C-C-plus-plus/GCC/cc1/index (Emphasis mine)

cc1 is also referred to as the compiler proper.

cc1 preprocesses a c translation unit and compiles it into assembly code. The assembly code is converted into an object file with the assembler.

Earlier versions of cc1 used /usr/bin/cpp for the preprocessing stage.

https://renenyffenegger.ch/notes/Linux/fhs/usr/bin/cpp (Emphasis mine)

The preprocessor.

cpp is not bo be confused with c++.

The preprocessor is concerned with things like

• macro expansion
• removing comments
• trigraph conversion
• escaped newline splicing
• processing of directives

Newer version of gcc don't invoke /usr/bin/cpp directly for preprocessing a translation unit. Rather, the preprocessing is performed by the compiler proper cc1.

I would almost consider this as a dup of this, but it's impossible to create cross site dupes. Relationship between cc1 and gcc?

Related: 'Compiler proper' command for C program

and what does "1" means in cc1, why it is called cc1, not cc2, cc3 ...etc?

Don't know. My first guess was that they just added a 1 to cc which was and is the standard compiler on Unix (excluding Linux) systems. On most Linux system, cc is just a link to gcc. But another good guess is that it stands for the first phase in compilation. Have not found a good source though.