Motorcycle gloves are there to protect you in an accident, but they're also going to make your riding more enjoyable by shielding you from the elements. And they do it while giving you enough sensation to steer your bike and operate the controls.
In an accident, our instinct is to put our hands out to break our fall. Asphalt running underneath you at motorway speeds will quickly erode any skin that touches it.
Gloves usually have palms made of a substantial material to resist abrasion. They may also have extra protection on the ball of the thumb, and pads or even plastic sliders on the heel of the hand. The palm could include foam or gel to absorb vibrations from the handlebars. Some gloves have sections of silicon to aid grip, particularly on the index and middle fingers for operating the brake and clutch levers.
On the back of the hand, there's often tough knuckle guards made of polycarbonate, kevlar or carbon fibre. Sometimes there's also smaller protectors half way down the fingers made of the same material.
Generally, gloves are either leather or textile, or a mixture. Leather is generally tougher, which is why textile gloves may still have leather on the palms for abrasion resistance. Leather gloves can be tough and inflexible at first, but will soften up over time as you use them.
When trying on gloves, you should go for the tightest gloves that are comfortable. If your gloves are too loose, you aren't going to have as much control input as you would in gloves that fit correctly, particularly with leather gloves which will loosen further.
Most riders end up with several pairs of gloves that they swap between depending on the weather. If you're just starting out, you could choose either a pair of all-season gloves or go with a pair each of dedicated summer and winter gloves.
All-season gloves often have a waterproof liner and a light thermal liner so that your hands stay warm and dry in spring and autumn. In the summer though, these liners can get stuffy and contain the sweat. In winter, those liners aren't thick enough to keep you warm and comfortable. If you are going to stick with a single pair of all-season gloves, you could consider a set of heated grips which will extend the usability into winter.
Summer gloves are often short, with the cuff either stopping on or before the wrist. This allows air to flow up the sleeve of your jacket. They aren't usually waterproof and often are actually perforated to allow air through and let sweat out.
Winter gloves usually have a long cuff, to the extent that they can be referred to as gauntlets. Your instinct will be to wear the cuff outside the sleeve of your jacket, but this just causes rain to run down your sleeves and into your gloves as soon as you stop. Like all-season gloves, winter gloves have a waterproof liner and a thermal liner, but they'll be thicker and warmer. They could have extra features such as a small wiper blade on the index finger for wiping rain off of your helmet visor. When trying on winter gloves, you need to make sure they aren't too tight - the waterproof membrane won't relax through use, and the thermal linings need to be able to expand enough to contain an insulating layer of air. Plenty of space near the fingertips will also aid circulation.
As with all gear, your best bet is to do some research, pick a few pairs that you like, and then try some on. Fitment is important for all gear, but especially so for gloves because you just aren't going to get the benefits if they don't fit right.