FormID
Form ID
An object's Form ID is a hexidecimal number used to refer to the object from within Oblivion. Within the CS (for scripts and such), an object's Editor ID can be used to refer to it, but you must use the Form ID for console commands.
Finding the Form ID
By default, the Form ID column is hidden in the CS. The Form ID column is located to the right of the Editor ID column. Refer to Image 1.
The double column line means that a column is collapsed there. Click and drag on the column heading to expand the column. The expanded column is shown in Image 2.
In this case, the Form ID for GiantSwordOfPwn is "02000CE8".
The Form Id can then be used in console commands as such:
player.addItem 01000ce8, 1
FormID Format
The first two digits in the FormID reference the source of the object. "00" is Oblivion.esm. "FF" (255) is used internally by saves. Anything between those two values is assigned dynamically based on the order the plugins load - if you've written down a FormID from your mod and it isn't working in game, it's probably loaded in a different order than it did in the CS.
The other digits differentiate specific things within each master or plugin file.