install GTK ?

I'm trying to compile some application in the Terminal and here is what I get

cd src && make
cd tilem && make
gcc -g -c -Wall main.c `gtk-config --cflags`
/bin/sh: line 1: gtk-config: command not found
main.c:21:20: gtk/gtk.h: No such file or directory
main.c: In function `main':
main.c:44: warning: implicit declaration of function `g threadinit'
main.c:45: warning: implicit declaration of function `gtk_init'
main.c:54: warning: implicit declaration of function `exit'
main.c:59: warning: implicit declaration of function `gtk rc_parsestring'
main.c:68: warning: implicit declaration of function `gdk threadsenter'
main.c:69: warning: implicit declaration of function `gtk_main'
main.c:70: warning: implicit declaration of function `gdk threadsleave'
make[2]: * [main.o] Error 1
make[1]: * [xtilem] Error 2
make: * [compile] Error 2

Do I need to install GTK ? How do I do this ?

Thanks !