I can't record my call or someone else's call with HUD

Recording is a Call Center Edition feature.

Recording from HUD requires HUD Agent, Call Center, or Queues.

Record on-the-fly for your extension - click the grey record button to the lower-right corner of your name.
Screenshot showing the record button

Record other's calls - click the red recording button under their name.  The button is only shown when they're actively on a call.

Recording is a permission that must be configured under the Web Admin Panel -> extensions -> group (permissions) tab.

Please read Permissions Definitions for detailed instructions about the permissions system.

Reference

See the various HUD Agent / Call Center Edition features in action.  This video is only a few minutes long.  I recommend showing it to your employees, or e-mailing them the link and instructing them to watch it.
HUD video tutorial for the Call Center