This is not going to be a comprehensive description of Daesh; it's rather an analysis that breaks Daesh down to an abstract level that's of interest from a particular perspective.
Daesh is commonly referred to as if it was a homogeneous entity, and from this fallacies such as the idea that bombing Daesh in Syria and Iraq would help fight errorism in Western countries stem from.
There are (as far as I can tell) three distinct faces of Daesh from the counterterrorism point of view:
(1) Daesh, the civil war faction and proto-state in Syria and Iraq
(2) The largely Daesh-indipendent jihadists (in the broadest sense, including loudmouths) overseas, and of particular interest:In the Western world.
(3) Daesh agents; charismatic zealots sent abroad by the Daesh leadership to build cells if not entire civil war factions in some Muslim country
It's noteworthy that #2 includes all those people who would have sworn allegiance to AQ and Usama Bin Laden only a few years ago.
Daesh has a problem in its civil war activities; it's killing almost exclusively Muslims, and at most some Muslims of a different sect or with less radical spirituality. This is bad from a Jihad point of view; from that point of view, they ought to kill non-Muslims, not followers of Muhammed. They're thus desperate to build the fight against such infidels into their brand, and category #2 provides the useful idiots who do this. The more attention they get for their activities, the better for Daesh recruiting of zealot mercenaries for the civil war forces in Syria and Iraq.
Category #3 is divided between those agents sent to Muslim countries and those sent to Western countries; so far the latter group is almost negligible. It's only this tiny latter group (and charismatic zealots who are not totally known to Western intelligence services are extremely rare) that's potentially going to cause trouble (errorism) to the Western world. The charismatic zealot agents sent to create a Daesh metastasis in a Muslim country are not the problem of the Western world, except potentially Turkey, Albania, Kosovo and Bosnia. And frankly, I don't think they would last long in Kosovo considering its powerful underworld.
The allergic reaction of the Western world to the murders in Paris is playing into the hands of Daesh. Daesh WANTS us to oppose them because they WANT to be seen as opposing us. Nothing would be worse to them than 24/7 news reports about how Daesh kills scores of devout Muslims in a perfectly secular struggle for individual power of its leaders!
The West's primitive allergic reaction also fails to reduce the threat from errorism (much less being efficient compared to other life-extending policies) because bombing category #1 means to bomb a civil war faction and proto-state, not bombing noticeable quantities of terrorists that would strike against the Western world.
Then again, it's not strategy what the Western countries do. It's the primitive, intuitive reaction of cavemen. They got and get played by a Daesh leadership that's smarter than them. Daesh will ultimately fail with its outright ludicrous exaggeration of the German mistake of accumulating too many enemies at war in parallel, but it does much more harm to us in the West in the process than is unavoidable.