command_echo:
    echo "hello world"

command_dependency: command_echo
    echo "hello world again"

TEXT = "test"
command_test:
    echo $(TEXT)

%.o: %.foo
    fooc $(FOOFLAGS) -o $@ -c $<
Then, whenever make needs to build xyzzy.o, and there is a file named xyzzy.foo, it will use that rule to compile it.

all: library.cpp main.cpp
In this case:

$@ evaluates to all
$< evaluates to library.cpp
$^ evaluates to library.cpp main.cpp