Is Acera m4000 usable for trails Can I use Acera m4000 on trails without damaging anything on my bike specially my derailleur
Acera is considered to be the entry level MTB groupset. It will be fine off road riding within limitations. 

More expensive group sets tend to be lighter weight, with more refinement - things like bearings in stead of bushing, seals to keep dirt out etc. As such the more expensive groupsets are more durable (to a point where the race focused stuff saves weight to sacrifice durability)

The main problem you will face is the components will wear out quicker than if they were higher quality, however if you wear them out, its a sign your riding enough to justify spending the coin on higher quality. 

The other problem you may face is that it will become trickier to tune as it wears out and may ot stay tuned as long as better quality components. This can cause breakages if poorly tuned and poor riding techniques combine att he wrong time time (e.g. power while shifting). You may need to tune the bike up a bit more often.