madhuras,

It would help if you outlined what you did when you tried...

Applying chroma key effect to a clip or image makes typically one color transparent so that you can see through to the object above (lower number track) it. A typical setup might be something llke:

• Track 1 -- a video of people at a picnic
• Track 2 -- a butterfly against a plain blue background

Apply blue chroma key to the butterfly object and the insect will appear in your picnic scene (size and position adjusted as needed) without its blue rectangular background.

Hope this help get you started.

Note: saying thanks is mush appreciated, but it would be better to 'Answer' your own original question so that the thank you appears and as additional entry rather than a completely separate posting.

Regards,

Carl