Resource Management
Any work done with the GameStart editor is done in the context of a project. While not a strict requirement all your project resources should be organized inside the project directory.
Project portability.
The resources of an application are best kept under the project root directory. When referring to a resource located inside the project tree its relative path to the project tree root can be used. Doing so makes the project portable from one system to the other.
Hint: You may move and edit files in the project tree using any tool you want. The editor will ask you to remap modified resource paths when opening them (eg. if you move or rename a texture referenced by a geometry, the editor will ask for the new texture path during the next opening of the geometry).
Importing a resource can also be done by drag-n-dropping it on the project explorer tree. Depending on the resource type the editor will take different actions (FBX will be converted to native scenes while pictures will be directly copied inside the project folder).
Working with resources outside the project folder.
Development versions of the project assets are usually kept outside of the project directory. Most of the time these assets are not stored in a format directly usable by GameStart and need to be converted before being used.
However, nothing prevents you from referring to a resource using its absolute path. Be warned however that you will loose all portability by doing this and that you will also prevent proper installation of the project (even in published form) on other computers unless the exact same file structure is reproduced.