XC401 question

[WildWiredWacky]

Hi, all;
when I un-tar XC40-1 tar ball, it extract the file to /xc directory. =20
But there is X11 default directly /usr/X11R6.

What is the difference? when compile program, how the compiler knows
which one should use.  Do I need merge
them or let the PATH poinst the correct path?

Thankx