Multiples animations in a single blend file For a University project I need to make a fish (guppy), create bones, add them to the mesh, create some "realistic" animations on the timeline, and finally redo the last point to be able to set multiples different animations on the fish to call them when needed from Unity Engine.

The fish and bones are almost okay. I linked them to the mesh and made animation on the timeline too.

However, I am not sure about how to manage the part when E need to make multiple animations. I have read that can be done with the NLA-Editor, but I do not understand how to do this. Can anybody explain me (an example is okay too) how the NLA-Editor works?

And for the bonus question, if some of you are Unity users, is it easy to call one of the different animations at will ?
You can save multiple animations (called Actions in Blender) for a rig by using the Dope Sheet and changing its context to Action Editor (switched with a dropdown menu in the Dope Sheet's header). From the Action Editor, each animation can be stored as an Action datablock (the same way you can have multiple mesh or material datablocks).

Important: If you store multiple actions make sure you give each action a fake user by clicking the F button to the right of the Actions datablock in the Action Editor's header. Failure to do so will result in you losing animations after saving and closing Blender. This is because all datablocks without users (including Actions) are purged when a file is saved and reloaded. Giving the action a fake user prevents that from happening.