On this inexpensive television, the back panel has two HDMI inputs (upper right), one component (green, blue, and red), and an antenna input. The optical connection is an output. The "IR Blaster" is so this TV can control other devices.
This is a slightly more advanced TV's back panel. On this particular TV, the HDMI inputs are on the side. The PC input is the same connection found on most computers, also known as RGB-PC or D-Sub 15. Check your TV's owner's manual to find out what resolutions this input can support (if so equipped). It may not even be 1,920x1,080. The "Video In 1" is the composite input, and is not HD.
Most new Blu-ray players will only have HDMI and composite (standard definition) video outputs. Don't be fooled by the cables included with the player. The yellow composite cable should not be used as it is not HD. The LAN connection is for your home network, which might get you better performance than Wi-Fi.
All HDMI inputs should work the same (except with 4K, see below). Many new TVs allow for labeling of inputs, so you can set "Input 1" as "Cable" or "Input 2" as "Blu-ray." You could label Input 3 as "Bob" if you want to confuse people. You know, for fun.
In case you're wondering, "ARC" stands for Audio Return Channel. It allows this particular input to send audio back to an AV receiver over the same HDMI cable that is carrying video from the receiver to the HDTV. That's useful if you're using your HDTV's over-the-air tuner or perhaps one of its built-in streaming media services (such as Netflix or Amazon VOD), and want to listen with your surround-sound system. The receiver--or sound bar or home theater system or whatever--must also support ARC for this feature to work (more info).
Not all HDMI inputs on 4K TVs will work with all versions of 4K. Check out HDMI 2.0 and HDCP 2.2 for more info. Chances are all your TV's inputs will work with 4K Blu-ray players and media streamers, but if you're having an issue, check your owners manual as one input might work with 4K, and another might not.
These are component cables. Note they have red, green, and blue coloring. They're also labeled Y (green), Pr (red), and Pb (blue). These three cables are all for video. Audio has to be hooked up separately. These are rare, as HDMI is easier and capable of higher quality images.
A common mistake with component cables is accidentally plugging a cable into the wrong input jack (i.e., red to blue or blue to green). If your picture has weird colors, or you're not getting a picture. Double-check that each output is going to its corresponding input.
The dreaded composite cables. This is a single yellow cable for video, and a pair of analog audio cables (red and white). As mentioned in the text, composite is standard definition only. Don't use this cable unless you have to.
These are composite inputs. You should never use them. OK, not never. Hardly ever. Old VCRs and the Nintendo Wii are the only sources you're likely to have that can use composite. Even the Wii can look better if you upgrade to component cables.