@geetakrishna there are many OER repositories that you can submit your resource to. @tmays had shared the Fiji OER site: https://fji.oer4pacific.org/. The focus for this course is to create open resources to be able to populate such repositories. Once your resource is submitted and approved, you can then provide a link to that particular resource in your documents.
@geetakrishna The lesson plan requires URL for external resources that will be used to deliver the lesson you are creating. So for instance, if you are creating a lesson plan to teach supply and demand, you would be including URLs for the resources that will assist in teaching that particular concept. The URL required is not for the lesson plan you are submitting but for all the resources you have included in the lesson plan. Hope this clarifies it further. All the best.