Record players need amplification. As modern home audio systems gravitated toward audio inputs from CD, DVD and MP3 players, the once-essential phono input used for record players began to disappear. This is a problem for turntable owners with modern audio setups. Those newer devices, like CD players, use line level audio inputs to transmit analog signals, while some devices, like microphones and record players, output at lower levels. Audio receivers with dedicated phono inputs typically include preamplifiers to boost those sound levels up, but newer receivers often don't include phono inputs. Without a preamp, a record player plugged into one of those receivers will sound mighty quiet.
Luckily, many record players include built-in preamps to boost their audio levels before transmitting a signal to an audio receiver or speaker setup. These record players, like the Audio-TechnicaLP120, will advertise a "phono preamplifier" as a selling point. A built-in preamp removes the hassle (and added cost) of buying an independent preamp, but some hi-fi audio fans prefer to have dedicated preamps that don't share a power source with the record player so they can fully customize their setup. Also, as more expensive record players generally offer a greater selection of features than cheaper ones, you may have to buy a pricier player if you care about a built-in preamp.
Modern record players also offer an option that wasn't available during the height of vinyl: USB connectivity. USB turntables can output an analog audio signal like their older counterparts, but they also offer the ability to plug into a computer's USB port and play audio through connected PC speakers. Of course, the major advantage of USB connectivity is audio recording. A USB turntable makes it easy to play an album and record it on the computer. That recording can then be converted into MP3s or burned onto an audio CD.
Aside from those special features, two important record player components -- the tonearm and cartridge -- come in different configurations. You might think one record player needle is like another, but cartridges come in a variety of styles. Picking the right one matters.