Re: Need to know how to add description to the Static routes in EX 3300

It's called annotation

https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/junos-software-configuration-comments-adding.html

in your case:

1. Create static route

set routing-options static route X.X.X.X/30 next-hop Y.Y.Y.Y

2. Enter to edit mode "routing-options static"

edit routing-options static

3. Annotate routes.

annotate route X.X.X.X/30 "STATIC ROUTE TO X.X.X.X/30 via Y.Y.Y.Y"