When you Google baby carriers, you will come across a million and one brands and types. While there are some hybrid carriers nowadays, the broad categories are:
Wraps are extremely comfortable and adjustable but do take some skill to get right.
Ring slings are worn diagonally like a messenger bag and adjusted by (you guessed it) two rings - you may have had belts that tighten the same way. They’re a really easy and comfortable way to carry tiny babies who aren’t ready for a buckle carrier yet. They’re cooler than wraps (as it’s just one layer) and they have a shorter learning curve.
Buckle carriers (also called soft structured carriers) are the ones you most commonly see - like backpacks for babies. They usually buckle around your waist and between your shoulder blades. They’re quick and easy to use.
T-shirt carriers have the comfort of a wrap with the ease of a buckle carrier and can fit tiny babies just as well as ring slings. They’re worn like a t-shirt (so it’s critical to get the right size) and they’re effectively a pre-wrapped wrap.
Typically, most parents will use a buckle carrier and then have a second, softer carrier (either a wrap, ring sling or t-shirt carrier) which really shine during the fourth trimester.