The reference platform for NGSPICE is a Linux system with glibc2 ang gcc (2.95 o newer) running on the i386 architecture. If you have such a system you can pretty sure that NGSPICE will compile correctly.
Once configured, to compile NGSPICE cd into the top level directory (if you moved from it after configuration) and issue the make. If you have a multi-processor machine, you can add -j3 to speed up compilation.
NGSPICE compilation takes several minutes on an average machine, enough to let you have a lunch. Once NGSPICE has been compiled, you have to install it issuing the command make install. NGSPICE will be installed under /usr/local/.