Tables used to be the only option. Today, the majority of scuba divers wear a dive computer and it makes sense.
A dive computer tracks your depth, time, ascent rate, and NDL in real-time. Dive tables are a fixed calculation. When you move between depths partway through, the computer recalculates. Tables are set before you get in.
Wrist computers are the most common use these days. They're small enough, easy to read, and you can wear them as a watch too. Console models are available but less people choose them now.
Basic computers run about a few hundred dollars and do everything a recreational diver needs. Features include depth tracking, bottom time, no-deco limits, log function, and often a simple freediving mode. The $500-800 range includes air integration, nicer displays, and more nitrox modes.
What new divers overlook is conservatism settings. Certain models are more cautious than others. A cautious other info algorithm means less no-deco time. More aggressive algorithms allow longer bottom time but with less safety margin. It's not right or wrong. It just your style and experience level.
Check with someone at a local dive store who's used various models first. They'll have real-world feedback on what's good and what's hype. Decent dive shops publish buying guides and comparisons on their websites too