1.Can we add digital books (e books) to koha as well?
You can add MARC records for digital books but Koha does not store the books themselves. We add MARC records for the resources we get from other providers and link to the source via the 856 tag: https://search.myacpl.org/cgi-bin/koha/opac-search.pl?idx=kw&do=Search&limit=mc-ccode%3ADNLD&sort_by=relevance
2. How to link this koha catalog to website?
Are you asking how to add links from your Koha OPAC to another web site? If so, you can use system preferences like OpacMainUserBlock to add HTML to various areas of the OPAC: http://translate.koha-community.org/manual/16.05/en/html-desktop/#editableop...
3. My uploaded list of. Oils doesn't show any covers. I fetched them from Amazon and had a link of that in book list. I don't know if it works like that.
If you have the OPACAmazonCoverImages system preference enabled Koha will try to find a cover from Amazon based on the ISBN in your MARC record: http://translate.koha-community.org/manual/16.05/en/html-desktop/#OPACAmazon... If the ISBN isn't found, nothing will show. I hope that helps, Owen -- Web Developer Athens County Public Libraries http://www.myacpl.org