Tattoo tubes cover the tattoo needle during that machine's operation and provide the artist a solid point for gripping the machine. There are different types available, but the main distinction to consider is whether you want reusable or disposable tattoo tubes.
Reusable tattoo tubes are made of stainless steel that can be autoclaved between uses, reducing the cost of your tubes over time. They are slightly heavier than disposable tattoo tubes, but offer more customization options, since they can be paired with the tattoo grips and tattoo tips that suit your needs and preferences as an artist.
Disposable tattoo tubes are made of plastic and individually sealed in sterile bags. While you'll need to continually purchase new tubes, you'll never have to worry about properly disinfecting them. Disposable tattoo tubes generally combine the tube, grip and tip into a single object, meaning that they are less customizable. But they're also light and there are so many styles available that you're likely to find one that suits you.
Tattoo grips are exactly what they sound like–a grip that wraps around a tattoo tube to provide an ergonomic, controllable point of contact with the tattoo machine. There are tons of reusable stainless steel and disposable tattoo grips out there.
When shopping for tattoo grips, it's important to know what machine you intend to use them for, since many companies like Peak, FK Irons, and Revol now manufacture adjustable grips for their specific lines of tattoo machines.