Flavor is a minisite based theme while Explicit is category based. So you need to make some changes and those changes are mentioned in the support documentation under Migration. And once you acivated Explcit you can switch back to Flavor any time. Everything will look similar, however the design will surely change.
It will definitely take some work on your part to get it up and running from Flavor to Explicit. You won't lost your posts, you will need to convert them. Here's the migration guide Kinshuk was referring to: http://www.industrialthemes.com/explicit/support/documentation/#migrating
Understood. So Ministes are no more then? Everything will display in the posts tab?
Yes, that is correct.
Is there a way that I can use the new theme but not activate it until I have it ready to activate?
One way is to create a copy of your WordPress install and do all of your edits there and then move it over when you're ready to go live. This is basically creating a development and live version of your site (basically creating a "staging" site) which is the recommended way of doing it. I believe there are also plugins out there like Theme Test Drive which let you preview what a theme will look like on your site but I think that's probably only good for seeing designs, not actually staging your site.