Your index.htm page should go in the public_html folder to be viewable when people surf to your URL.
You can then create sub-folders in public_html and put index.htm pages in them. If you have an on-line resume, for instance, you can create a folder named "resume", then put your resume in that folder and name it index.htm. Then when people surf to
http://www.yourdomain.tld/resume it will load.
You could have everything in the public_html folder and put links on your index page, but it sometimes slows down loading of the public_html folder when you are using CPanel or FTP. So most of us have a "images" folder, a "forums" folder, etc.