Why do we need to build telescopes that can view in the infrared? What exactly do we need to see in the infrared region? I know this seems like a really broad question but I'm just curious about it.
Three main reasons.
Lots of things in the universe are cool, much cooler than the Sun. Therefore they emit most of their radiation in the infrared spectrum. Examples might include brown dwarfs, giant exoplanets, circumstellar discs.
Lots of things in the universe are distant and highly redshifted. Thus even if they emit their radiation at visible wavelengths, we receive it at infrared wavelengths.
Lots of things in the universe are hidden by dust, which effectively absorbs visible light. Dust is much more transparent to infrared radiation, so we can see beyond it. An example would be the centre of our Galaxy.