The .a
extension indicates that it is a static library. So in order to link against it you can use the switches for the linking stage:
gcc -o myprog -L<path to your library> main.o ... -larchive
Generally you use -L to add the path where libraries are stored (unless it is in the current directory) and you use -l<libname>
to sepecify a library. The libraryname is without extension. If the library is named libarchive.a you would still give -larchive.
If you want to specify the full name of the library, then you would use i.e. -l:libname.a
update
If the libraypath is /usr/lib/libmylibrary.a
you would use
-L/usr/lib -lmylibrary