something is terribly wrong with pkg-config

I've been having a harrowing time lately just trying to get several C programs compiled because I can't find where the libraries are located and pkg-config seems to be out of order. I installed GNU GSL like this: wget ftp://ftp.gnu.org/gnu/gsl/gsl-1.15.tar.gz tar xvzf gsl-*gz cd gsl-1.15 ./configure make sudo make install Apparently it installed in /usr/local/lib which is a non-standard place? (1) What is a standard place? (2) How would I get it to install there? And I can't manage to compile a simple program that uses this library: $ gcc gsl_erf.c -o gsl -I/usr/local/lib -L/usr/local/lib /tmp/cc3WD9Zq.o: In function `main': gsl_erf.c:(.text+0x24): undefined reference to `gsl_cdf_gaussian_P' collect2: error: ld returned 1 exit status Now, with pkg-config : pkg-config --libs --cflags gslPackage gsl was not found in the pkg-config search path. Perhaps you should add the directory containing `gsl.pc' to the PKG_CONFIG_PATH environment variable No package 'gsl' found So I did add the directory: PKG_CONFIG_PATH=/usr/local/lib/pkgconfig But no luck yet! :( pkg-config still gives me the same message as above. (Perhaps you sh ...) This is a more general problem I face regularly when I have to compile some C program. I would love a general solution for: 1. Where and how do I install my C libs? (Perhaps the same place yum installs them?) 2. How do I correct/configure and use pkg-config ---- **Update** : I tried one of the answer's suggestions below and running the compiled program gives me this : ./gsl_app: error while loading shared libraries: libgsl.so.0: cannot open shared object