when we come to PLP page of any Category it shows only Product name and price i need to show description as well on plp.
You'd have to override the ProductWidget template, which uses the product-item molecule.
The product-item template is also used in the PDP. If you don't want to override the product-item, then you'd need to create a new molecule which could extend from product=item and then add the product description.
I think that the product description key is not available in PLP but only on PDP. In this case you need to also modify the SearchClient so as to return the description.
Take a look at the course : Frontend for backend developers. There you will find everything related to overriding templates, creating widgets and molecules