How do I upload video clip?

I want to upload a small video clip and have no idea how to do it. I also am in the dark about knowing how to play this video in game once i import it.

Can anyone help?

Basically, you don't.

Most video in SL is done by STREAMING, not uploading. You make a QuickTime video; most video editing software can export one. You put it on a server somewhere, and set the land media properties appropriately. Then you set up some sort of viewer in-world; many are available, including free ones.

You can create a VERY short low-resolution animated clip by using texture animation. For that, you might create a 1024x1024 texture and split it into smaller zones. 16 256x256, 32 256x128 (for widescreen video), or 64 128x128 areas are possibilities. (Yes, I know that it's usually best to avoid textures bigger than 512x512; this is one of the few legitimate reasons to use one.) You put one frame of your video in each zone of the texture. Then you can use llSetTextureAnim() to cycle through the clips. To see an example of texture animation at work, pick up a free candle somewhere, take it apart, and look at how the flame is done.