I have downloaded and unzipped PETSc from PETSc Website in my home directory (OS is CentOS 6.3 64bit )  and followed given commands on Installation page  ./configure --with-cc=gcc --with-fc=gfortran --download-f-blas-lapack --download-mpich and make all test. There was no error throughout the process. Is it installed properly? How should I start using these libraries in C programs? Is it possible to install it in file system? so that one can access it like LAPACK libraries or CGNS libraries.
About PETSc installation
petsc
If make test reports something likeRunning test examples to verify correct installationUsing PETSC_DIR=/home/nate/src/PETSc-3.3 and PETSC_ARCH=arch-linux2-c-optC/C++ example src/snes/examples/tutorials/ex19 run successfully with 1 MPI processC/C++ example src/snes/examples/tutorials/ex19 run successfully with 2 MPI processesFortran example src/snes/examples/tutorials/ex5f run successfully with 1 MPI processCompleted test examplesthen indeed the library should be installed properly. I would recommend that you export the values of PETSC_DIR and PETSC_ARCH (the ones that, for example, are shown when you run the tests) in your .bashrc file such that they are always set. With these environment variables set, you can use PETSc from anywhere if you use makefiles which look something like:MyCode: MyCode.o chkopts    ${CLINKER} -o $@ $< ${PETSC_LIB}include ${PETSC_DIR}/conf/variablesinclude ${PETSC_DIR}/conf/rulesIf you need to make PETSc available for all users on your machine (like in /opt) then just go to the PETSc installation page and look for the section labeled:Installing PETSc in /usr/local or /opt where sudo or root previledges are required