How to do what? @jaikrishna.t told you to upload to /htdocs, and you said you don’t know how. All you have to do is connect via FTP and upload the files to the /htdocs folder. The article tells you how to do that.
It would seem your website files are incomplete. Normally, the base folder of your website needs to have an index.html file.
How are you uploading the files by the way? Are you uploading them manually with FileZilla or something like that, or does your website builder have tools to automatically push your site to our servers?
If it’s the former, please double check that the folder with your website files has a file with the name index.html in it.