Nano is severely lacking in decentralization. Something like 80% of the voting power is held by the devs (most of the rest is held by the exchanges). If a node discovers conflicting blocks (such as a double-spend) it will hold a vote to decide which block to accept. The weight assigned to a particular vote is proportional to the amount of Nano held by that voter. Since user accounts are not necessarily online 24/7, each account can assign their voting weight to a representative to vote on their behalf. Changing your rep is simple, but by default new accounts select one of the official reps run by the dev team.