Charles - How to filter the recording using the "client address" field?

Under Proxy > Recording Settings

You can enter specific locations to exclusively record requests to/from using include, or exclude to prevent locations from recording. It's also possible to blacklist requests as needed by control-clicking in the structure section and selecting ignore. If you want to exclude requests to/from the computer that Charles is running on then you'll need to close it's web browser, email, etc. to keep internet requests intended to/from it to a minimum. You cannot ignore the host machine Charles is running on since it's used as the proxy — but you can selectively include/exclude other machines/clients by using access control.

To use Charles as a "Man in the middle":

Keyboard shortcut ⇧ ⌘ P, or choose from the menu use Proxy > Mac OS X Proxy.

NOTE: Option does not exclude (host) traffic incoming/outgoing on machine used as proxy.

Command+Shift+P should do the trick, or toggle off MAC OS X Proxy from the Proxy menu.

You can also disable the proxy for your machine. This way, the only connected client will be the ipad. On your Mac OS X, just go to System Preferences > Network > Select active network device > Advanced > Proxies and uncheck both Web Proxy and Secure Web Proxy