Is there a way to export GLTF or do I need a plugin or something? Thanks!
For Blender 2.79(x), use the Khronos Blender Exporter:
To install it, copy the
scripts/addons/io_scene_gltf2 folder to your
blender-2.79*/2.79/scripts/addons/io_scene_gltf2 folder. Then, re-launch Blender, go into User Preferences -> Addons, search for glTF, and enable the export plugin there. Please do read the plugin's documentation to learn how to author PBR materials in Blender that will survive the export.
For Blender 2.8 (currently experimental), there is a new project in the works now:
This is a refactoring of the exporter, combined with a new importer. It's still under development, but the goal is to make this compatible with Blender Eevee's Principled BSDF node, so that PBR materials can be exported and imported directly there. There will still be some caveats, as glTF 2.0 does not contain a node graph, but the general Metal/Rough PBR workflow should be working. Once the development efforts stabilize a little more, this will be contributed back to Blender for inclusion.
UPDATE, 2018-11-25: Blender 2.8 "experimental" builds, starting with this morning's build, now include the above "glTF-Blender-IO" plugin installed and enabled by default. If you get the latest build, you should find "File -> Export -> glTF" as an option, already enabled. At this time the plugin is still under active development, and glTF-related bug reports are welcome in the issue tracker.
You need to install a plugin. The official export plugin from Khronos Group can be found here.