Audacity is an open-source (free download), sound editing program that will give you a lot of options for sound editing.
How to Soundproof a Cardboard Box
There are several different methods for soundproofing for high quality audio production. This is one option.
Free Music Archive
Royalty free music files.
Royalty free audio clips. Great for adding ambiance to your podcast.
NPRs curriculum for educators on teaching podcasting.
Adobe Spark includes a free option and can be used to create video stories (and web pages and graphics).
How to Create a DIY Green Screen Video Effect
Information on creating the screen, taking video and editing.