Different theme "Template" for other pages

I want my main page to keep the menu/ look it has but have all other pages be clean without the menu/ pics of the front page. ie a different theme for other pages.

I have a sliding menu on my site that works well. But when I go to another page I want this menu bar to not be there – ie I want my content to fit on the page.

I think I need to give those other pages a different “template” or “theme”? Am I correct?

I have reviewed several posts. It seems like I could:

1) Add my theme as a child so I can edit it and add a “sub-template/ sub-theme”? But I have not found out how to save the theme as a child. Nor have I figured out how to add sub page themes/ templates to this so my other pages can “look” different.

2) Install WordPress a second time to my site with a different template/ theme. This seems the easiest but when I do this it says it will overwrite site. One blog suggested to install wordpress to mysite.com/blog so the customer would see blog.mysite.com. This seems to be the easiest but mysite.com/blog is not available at wordpress? Do I need to add it to my host company? Am I charged for this even though it is the same web address?

3) If I could get the site to jump to the middle of the page the the unwanted info could still be on the page but at least the customer would be brought to the important content.

I apologize I am new to this.

Thanks! Don