in the oven slowly or buy a dehydrator; I'd give you more info. if I knew what foods you are trying to dehydrate here are videos to sort thru-- https://www.youtube.com/results?search_query=dehydrating+foods
Here is a video tutorial for you: https://www.youtube.com/watch?v=FKSgyjk_e3c
I like having a dehydrator. They aren't very expensive. I prefer the ones that have a fan and heating element both. It's really important to make the food pieces as uniform in size as possible. I also rotate the trays every couple of hours to even out the drying
What type of dry food are you wanting to can? Perhaps it is better to freeze, or to vacuum seal it in the thick plastic bags?
Is the food being purchased already dried, or will you be using a food dryer (shown in Celebrate's posting above) first?