In democracy, power is transferred according to set rules. The transfer occurs via a vote of the people. Sometimes it can be complicated (as in the hung election in Australia right now) but even then it follows established rules and is based to some large extent on the popular vote.
In an autocracy, there are not any rules. The transfer of power is often violent. When an autocrat dies or is dying, others will vie to take power. This is sometimes only a political competition, but it sometimes involves violence. Transfer of power can be accomplished peacefully if the autocrat picks a successor who commands enough respect to be allowed to rule in their own right.
Power or authority to govern a country or state is conferred upon representatives of the people on the basis of election. These elections are held generally ad fixed intervals such as every four or five years. A group of people, generally belonging to a political party or a coalition of multiple parties with greatest number of elected representatives form the government. These elected representatives may then select leader among themselves to head the government. Alternatively the head of government may also be elected directly by people.
In a democracy, when a party or a person is elected to power in an election, the existing persons forming the government resign and transfer to power to newly elected government peacefully in line with the procedures laid down in the constitution and other laws of the land.
In an autocracy, the autocrat generally do not like to relinquish power or transfer it to any one. Frequently power is transferred to another person,only upon death or violent over throw of the existing autocrat. In limited case the autocrat may name a successor during his life time and even install such a person to run the government even before this or her death.