Help Modifying Makefile to compile additional code

[Emil808]

I would like advice on how to add additional custom code.

The structure I am working with now is:

/software/hello
Here, where the main function is located, and uses code from headers defined in:

/custom-software/custom_header.h
/custom-software/custom_src.c

I'm overwhelmed by this bigger code base, so how do I modify the current make file that shown bellow to compile and include the custom software that I made. I tried looking at makefile tutorials but having a hard time understanding how to adapt it to the freedom-e-sdk setup.

$(PROGRAM): $(wildcard *.c) $(wildcard *.h) $(wildcard *.S) 
	$(CC) $(CFLAGS) -Iinclude $(LDFLAGS) $(filter %.c %.S,$^) $(LOADLIBES) $(LDLIBS) -o $@

clean:
	rm -f $(PROGRAM) $(PROGRAM).hex