How to start in animating model?

The quickest and easiest way to animate a model is to upload it to Maximo and use the autorigger, then add some of their animations. If the model is less than 10,000 polygons, then it's free, and about a dozen animations are free as well. What I do is animate the model with each animation I want one at a time, then have four or five of the same model with different animations, import them to Unity, click each animation file and click edit-duplicate. Rename the animation file to something better than maximo and script a js file to play the animation per action (i.e. walk, run, dance, fire, jump, etc.)

I'll write up a simple animation script and post it below if you want to use it, then just attach it to the character/model you want to animate.

p.s. Be sure to set the animation to Legacy under the rigging tab (click the imported models prefab, select rigging, and choose Legacy, then under the animation tab select import animations).

 public var walkAnimation : AnimationClip;
 public var idleAnimation : AnimationClip;
 public var fireAnimation : AnimationClip;
 
 
 function Start () {
    animation.wrapMode = WrapMode.Loop;
    animation[fireAnimation.name].wrapMode = WrapMode.Once;
    animation[fireAnimation.name].layer = 1;
    animation.Stop();
 }
 
 function Update () {
 
    if (Mathf.Abs(Input.GetAxis("Vertical")) > 0.1)
       animation.CrossFade(walkAnimation.name);
       
     else  if (Mathf.Abs(Input.GetAxis("Horizontal")) > 0.1)
       animation.CrossFade(walkAnimation.name);
       
    else
       animation.CrossFade(idleAnimation.name);
       
    if (Input.GetButtonDown ("Fire1"))
       animation.CrossFade(fireAnimation.name);
       
    if (Input.GetMouseButtonDown (0))
       animation.CrossFade(fireAnimation.name);
 } 

If you need a separate animation for walking backwards, then add a new line under:

 if (Mathf.Abs(Input.GetAxis("Vertical")) > 0.1)
           animation.CrossFade(walkAnimation.name);
 
 

like this:

 else if (Math.Abs(Input.GetAxis("Vertical")) < 0.1)
           animation.Crossfade(backWalkAnimation.name);
 
   

and in the public var at the top:

 public var backWalkAnimation : AnimationClip;
 
 

The same goes if you want a strafing animation for "Horizontal"