From BlenderWiki

[edit] What's an IPO curve?

IPO means InterPOlation. IPO curve defines interpolation of animatable attribute such as location, rotation or color. You can edit IPO curves in Blender's IPO Curve Editor window.

[edit] How do I add a new IPO curve?

You can keyframe (i key) an attribute or select the ipoable attribute in the IPO curve editor and then use ctrl-lmb to add a curve. For instance if you have a cube selected and you want to add LocX IPO to it, select that IPO at right in the IPO curve editor and ctrl-lmb on the IPO area. You can add more points to the curve in same way.

[edit] How do I edit an IPO curve?

If you want to edit the currently selected curve(s), use tab to enter edit mode. Use tab to exit curve editing mode.

[edit] How do I delete an action?

Blender automatically creates 'fake-users' to actions, so that they can be stored in blend files as a library of actions. This is the reason why you cannot delete them by using x button in the action editor. Pressing x button there just disconnects the action from the currently selected object.

To really delete actions you must first remove references to them (see 'action contstraints', 'action windows', 'nla strips', etc.). After that hit shift-F4 and go to a folder called Action. Right click on the names of the actions you want to remove and press f key. The number of users should change to zero now. You can see this in the Data Select window.

In Blender unlinked objects\actions\... get deleted when .blend file is closed so close the file and open it again. The actions should be gone now.