Start by dragging your animation FBX into the content browser.
- Click on the animation in your asset browser
- In the inspector, convert rig to humanoid.
- Click configure and make sure the skeleton is in a perfect T pose.
Next, create an animation controller. Go to assets -->create --> animation controller.
Then, click on your character in the hierarchy and add an animator component if there is not one already there. Set the controller to the controller you just created
Now, you need to add the animation to your animation controller. Double click on your animation controller in the asset browser to open it. Then, drag in your animation clip and connect it to the entry node.
Click on the clip and adjust the animation speed if needed.
Press play to test.