Light bulb socket adapted to a 3 pin plug socket
Hire a handyperson to do this.  Or at least, turn off all power before doing any work, and get up to speed with electrical safety by reading a decent book on DIY home electrical.
The fixture almost certainly is attached to an octagon box.
Remove light fixture entirely.  Then install any common receptacle in this style of octagon box cover

and fit it up to the light's junction box.
If you run a ground wire to the receptacle, then you can mount the recep to the plate with just 1 screw (the middle screw).  You need the 2 outer screws if grounding is coming through hard metal-metal contact between plate and box.
If your octagon box is 1/2&quot; too small for this type of plate, then you have a &quot;3-1/2&quot; size box, and that will require a very special plate that has (and includes) only 1 socket.