FBX ANIMATION

I have seen many fbx models online which contains a number of animations in it.I am creating an fbx model for unity and want to add more than one animation in my fbx model but unable to do that.needed help what I need to do so that i can get two or more than two animations in just one fbx model.
whenever I am trying to create a new animation for the character its creating another fbx file but I want to add more animations in one fbx.

Sorry it may be an amateur question, but how are you adding your animations?

I get my animations from mixamo, from there you can add the animation to an animation controller.

Not sure if this helps at all.