Although you may need to learn the traditional GNU Makefile syntax in order to work with other projects, I recommend using CMake for your own projects because it is simpler and more intuitive.
A CMake file for your example would go in a file called CMakeLists.txt
in the root directory of your project (same as the source in this case) and look like this:
project(HelloWorld) # Name your project.
add_executable(helloworld helloworld.cpp) # Specify an executable to build.
link_directories(/path/to/SFML) # Tell it where your libraries are.
target_link_libraries(helloworld Library) # Tell it which library to link.
If you want to be able to #include headers from SFML without including the directory name every time, then you can also write:
include_directories(SFML) # Tell it where your headers are.
Further documentation on writing CMake files and running CMake is available on the website.
Lastly, CMake often gives a noisy but harmless message requesting that you put a line like this at the top of your CMakeLists.txt file:
cmake_minimum_required(VERSION 2.8) # Quell warnings.
Cheers.