Programming :: Linking Object Files With Geany On Ubuntu - Undefined Reference To Class::functionName

I have created a simple test class - Mortgage, with the class declaration in the .h file and the class's methods defined in the .cpp file. (mortgage.h && mortgage.cpp, respectively) Straight up C++ 101 as far as I can tell. I instantiate the class in the main() function, which is defined in practice.cpp. Using Geany on Ubuntu, both the practice.o and mortgage.o files are created, but then I get a linker error: undefined reference to class::functionName

I get it for each function. If the mortgage.cpp file is foremost in the editor when I click "build", then I get the undefined reference to main() error, if practice.cpp is foremost (where the main() function is) then I get undefined reference to Mortgage::Mortgage(), and all the rest of the functions defined for that class. How do I get the linker to know where my object files are so it will link them in? Or is the problem somewhere else entirely?