question abour executable and lib

[eric]

i have a question about library

until now i have a code which is in two parts , than i compile 
separatly, mzking executables. The first one call the second one.

now, the second code will be out of my view and i will be given a 
library instead.

how can i modifie the make to use this library ? the first code will 
link with this library or can i change this library into an executable ?

thanks