"Remember Allah inspired the angels: I am with you. Give firmness to the believers. I will instill terror into the hearts of the unbelievers: you smite them above their necks and smite all their fingertips off of them." (Sura 8:12)
In the interest of fairness, some Muslims do not take this injunction as a command for present-day action because (a) Allah was speaking to angels, not men, or (b) this passage refers to a historical event (battle of Badr).
So when you meet in battle those who disbelieve, then smite the necks until when you have overcome them, then make (them) prisoners, and afterwards either set them free as a favor or let them ransom (themselves) until the war terminates.
Again, the ordinary Muslim does not read this and then goes out of the house, scimitar in hand, to smite unbelievers.
What the clerics preach is another matter. As we all know the Quran also contains peaceful passages, yet the orthodox Islamic interpretation is that many of them have been abrogated by more violent ones written when Islam had become more powerful.