You should read your owners manual or visit the Emerson home page.
From the Net:
Emerson LF501EM4 50" 1080p 60Hz Class LED HDTV:
50" LED panel
With a 1920 x 1080 Full HD resolution
True 16:9 aspect ratio
View your movies as the director intended Built-in digital tuner
Watch digital broadcasts, including HDTV programs where available
HDMI Inputs: 3
Enjoy a superior HD experience with HDMI, the one cable audio/video solution
49.5" screen measured diagonally from corner to corner
It depends on whether the TV is analog or digital. Picking it up at a yard sale could be that its analog, which you would need a converter box. Easy way to find out is hook it up to an indoor antenna and go to the TV menu and let it scan to find channels (assuming you have the remote and the user manual - you may need to google the TV brand and Model no. to find a manual on-line (and the universal remote codes if it had no remote). If it finds all your local channels (assuming they are nearby - 25 miles or so), then you have a digital TV and don't need the converter (unless you want one with a USB port to hook up to a jump stick or external HDD and record shows). BTW, most digital TVs will also pick up an analog signal, but very few TV stations transmit an analog signal anymore - those that do won't be your normal stations such as CBS, NBC, ABC, Fox, etc., which are all digital.