You have a range of ticket choices, from a single journey to a monthly travel pass, all of which are printed onto a magnetic card, bought from booths in the station vestibules. Though constantly rising, ticket prices are low by any standards, with a single journey to anywhere in the city costing less than 50 cents.
The metro works from 05.30 to 01.00 daily, and trains run regular as clockwork every three minutes during the day, and about every seven minutes late at night or very early in the morning. Interchanges between the lines are either between platforms at the same station, or between two stations with different names (the difference is only a matter of labeling really). Some stations have more than one entrance, so you need to know which street you want to surface on. All these things are made easier if you take the time to familiarize yourself with the Cyrillic alphabet (the transliterated maps on the metro trains are a good place to practice!).
The name of the next station is announced as the doors close before departure, and just before the train arrives. If you are going to St Petersburg, please note that the system there is completely different.