You can import files by drag and dropping them to a TouchDesigner network.
On the menu bar, import via File -> Import File... using the Import File Dialog
Geometry and scene files in FBX .fbx format are also imported through File -> Import File..., which will convert the .fbx files into the appropriate Object Components and SOP Operators. You can choose to import the camera, light and other data from the original file.
See also Import a GLSL Shader.