Keyboard Shortcut to Move Within a MacBook App

I use a Wacom tablet a lot, mostly for photography, and I also make a lot of use of keyboard shortcuts. One thing that I have not discovered a way to do, other than using the Wacom pen, is to move between parts (right name?) of an application. For example, in the Mail app, on the right I have a list of all my email accounts, flagged messages, mail folders, etc. At the top I have a list of all the email in my inboxes, and on the bottom I have a display of the current email I have selected from the top list.

When I move between the top list to the bottom list or the side list, I need to use the Wacom pen to tap on the section I want to work in.

My question ... in any MacBook app, is there an existing shortcut key, or one that I can create to move between the app sections (or whatever they are called). Other apps that I use a lot where this would help are reminders and notes.

Thanks for any feedback ... Jay-Dee Purdie