I'm not familiar with the particulars of your set, but I assume it has at least one pair of audio output jacks on the back, maybe even two pairs, one labeled "fixed" and one labeled "variable", perhaps. Some TV's accomplish the same thing with only one pair of outs. They instead allow you to select fixed or variable in the setup options. In either case, you're gonna have to connect one pair of these jacks to either an amplifier or to a set of powered speakers. The amplifier could be in the form of a receiver (amp/tuner/pre-amp), an integrated amp (amp/pre-amp), or a basic "power" amplifier. Most power amps will not have volume controls, so that option would only be practical if your TV has the variable audio output function. This would allow the TV to control the volume even when using the external amp to power separate speakers.
The simplest option is, assuming again your set has a variable output option, is just get an inexpensive amp and a pair of speakers, but in terms of value, you may find it preferrable to get a 2 or even 5.1 channel receiver instead. This would give you a remote for volume, in case your TV has only fixed level audio outputs, plus you would typically get an am/fm tuner and inputs for other a/v devices. And the 5.1 channel receiver can open up a whole new world of surround sound, in case you are so inclined.