In the project folder called Gestures / Prefabs you will see a selection of templates you can duplicate, rename and modify.
Highlight the 1 Person Template file and click ctrl D to duplicate.
Rename your new prefab in the project window, then drag it into the scene.
You can also create an empty game object and then add the specific Avatar Effect Scripts you require, and a Virtual Goods Script.
When you import the .fbx file containing your animation you need to rig it.
Click the rig tab in the inspector. Set the type to Humanoid. Set the Avatar Definition to Copy From Other Avatar Select the relevant Space avatar as the source (click the small circle to the right of the Source field.)
Now click from the rig tab to the Animations tab.
You should be able to see your animation in the preview window in the Inspector.
You may wish to crop or modify the animation using Unity's tools in this panel; see here for more information on Unity's animation tools.
The name and description fields in the Avatar Effect Script are for PENDING
Set the number of participants to 1. Leave the Trigger fields empty; these will be used with multi-person gestures. Tick loop if required; e.g. for dances. The user will be able to stop looping inworld.
Drag the animation take from within your fbx file into the Clip field. You can use the start time to delay the start of the gesture. If your gesture involves interaction with fixed position prop (e.g. a door handle) or with precise two person gestures (e.g. shaking hands) you may wish to tick Fix Avatar Height. This will set the user's avatar height to the standard height for avatars in Space.