Make sure you have the 'make' program installed as well as a c++ compiler 'g++' At the command line type:
make --version
g++ --version
You should see some version information about your c compiler and make instance.
First read the c++ source files. They're pretty simple. Then read the makefile.
Change directories into the folder with this README and run make main at the terminal.
After some output you should see a file appear in this directory called main.
Run it by typing ./main at the terminal.
Try changing the different source files and re-running make.
Try running make main then rm one.o then make main again. Look at which commands it runs. Notice it doesn't regenerate two.o.
Run make clean to reset the directory and remove all the .o files and the executable.
You can also look at this makefile tutorial to see a similar example worked out, and more features of make.