This is a question many ask when the majority of us already own a pair of road shoes, and this will of course involve digging into your pockets for the privilege. There is no doubt about it, buying a pair of trail shoes can be confusing when you are being asked about drop, lug height, cushioned or minimal, rock plates, uppers, waterproof or non-waterproof, heel counter etc etc, it can be overwhelming.
Trail shoes are designed to be more robust than road trainers, to allow for the impact of running on uneven ground which can put stress on the toes and sides of the feet.
If you're running in deep mud, then you will need a deep lug with good spacing to provide you the grip you would need to stay on your feet. On harder terrain, a shallower lug with a rubber sole would give you more grip and responsiveness.
Rock plates sit between the outsole and the midsole and give your feet protection from running on sharp or hard objects. Imagine running across Lego in bare feet, which of course hurts!
Waterproof shoes is another factor which depends on the environment you are running. To prevent your socks from rubbing and causing blisters when running through deep pools of water, a trail shoe with good drainage would be advisable. However, if your route mostly takes you through dew-covered grass or snow, waterproofing may be a better idea.
On harder, compacted trails, a cushioned shoe will help keep those injuries at bay, but in deep mud, you would be best going for a less cushioned and more responsive trainer. Also consider how firmly your foot sits in the shoe and how much it may move around due to the unpredictable terrain, as again, this is blister prevention.
The drop refers to the difference in height from the heel to the toe, which can range from flat to 10mm. Trail shoes generally have a lower drop than road shoes but this comes down to personal preference and doesn't necessarily mean more cushioning.
Considering all these factors, and your enjoyment in getting out on the trails, investing in a pair of trail shoes is well worth it. Running shoes unfortunately will not stand up to the stresses of trail running, and will quickly deteriorate. Work out the type of terrain you are likely to run on, and consider some trail shoes that would give you the grip and support to make your running lively and exciting.