If there's no UI and you are using straight C, select the "Standard Tool" project type. Put your source files anywhere you want under the Project name tab on the sidebar (you can organize its folders however you like). To compile, just select "Build", that's really all there is to it unless you need more advanced options (of which there are many). You can run it from Xcode or from Terminal (command-line). If I were you I'd download some example C Xcode projects from Apple or other sites and just look at how they are layed out.