Rephrasing it, you could say: "You're about to go and see what items are stored in your kitchen and get rid of all the items that you've never used and that you're unlikely to ever use". "taking an inventory" means making a list of what you possess. For example, a shop owner making an inventory, would be making a list or tallying all the things he has in stock. If I was making an inventory of my garage, I would be going in and making a list or seeing exactly what I have there. "clear out" means get rid of. Often it means getting rid of all the unnecessary things that are no longer needed. "I cleared out my garage" means I got rid of all the items there, or all the unnecessary items. "no longer serving you" means not useful to you anymore and no longer needed.

It means imagine the beginning of the song "Eye of the Tiger" or "The Final Countdown" playing in your head before you do the inventory of the kitchen and so on.