Inside a Russian Orthodox Church
I'll start with the gate, because normally, there's a fence surrounding the church grounds and possibly the cemetery if it's there. Unless it's in the centre of a big city where there's no space for a fence. There're two gates serving as the main entrance in the fence: a large drive-through one used by cars and (possibly) hearses, and a narrow walk-through one. So people are supposed to go through the narrow gate and not take the wide one. First, because of that saying that we should take the narrow path into the Kingdom of Heaven. Also, because of hearses using the wide gate, there's a superstition that the person who walks through the wide gate will die soon. :-)
There's always an icon or at least a large crucifix over each of the gates. You approach the gate, make three signs of cross bowing low to the icon or to the crucifix and walk through.
There's another icon (usually of Christ) or at least a crucifix over the church entrance. You do the same thing again, making three signs of cross and bowing low each time. You may touch the ground with the fingers of your right hand, but that's optional :-)
The door: normally, it's heavy double doors of oak or other hard wood, or in our days sometimes of steel to keep thieves out. There're all sorts of church-life related announcements pinned to the doors: scheduled services, christenings, choir and Sunday school meetings and such.
Once you're in, yes, there is a lobby (size varies), carpeted or not, where you'll see more announcements, as well as doors and stairs leading to offices, the choir loft and such. If the church is really small, the lobby is small, too, and its main purpose is to serve as an extra bit of insulation from winter frosts.
The double door leading from the lobby into the actual church (its purpose, too, is to keep the cold out) usually has glass panes in it. You walk through it. The first thing you do is make three more signs of cross bowing low each time. Then you start looking around :-)
To your left or right, just by the entrance, you'll see what they call a candle box: a stall or kiosk that sells candles (which are always thin and long), icons, books on religion and such. They also accept people's "notes": written requests to pray or hold a special service for a particular person or people, whether alive or dead. You always have to pay for those requests (unlike some Russian Orthodox churches here in the West that do it for free). You can also make all sorts of donations, buy candles to place them in front of the icons of particular saints of your choice, etc. I tell you, going to a Sunday service in Russia is not cheap!
But before you head for the candle box, you'll see a large icon placed on a lectern in the very middle of the church. The thing is, every single day in the Russian Orthodox calendar is dedicated to a specific saint or a Biblical / historical event, and the icon depicts this particular saint or event. So these icons are changed every day (or week, if the event lasts all week, like Easter) during the evening service. You approach it and do the same thing with three signs of cross and bows, and this time you kiss the icon.
(I wonder if you know but there's some scientific research that shows that even the most popular and therefore most kissed icons in Russian Orthodox churches are normally virtually bacteria-free; also, the ladies who supervise the church during the service clean them several times during each service.)
I do hope you know that nobody sits during a Russian Orthodox service? There're no pews, period. In the West, I've seen Russian Orthodox churches with pews but that's simply the cultural influence of other Christian churches and I personally think it's not a good idea. In Russia, no one would dream of sitting down during the service, but there's always a spare bench or two kept in the back for very old ladies or heavily pregnant women (an Orthodox service may last anything from 2 to 4 and more hours!). It's all right for them to sit down during some very strictly specified parts of the service.
Basically, each church is divided into three major areas: the centre, the right and the left half and often the architecture makes this division very clear by using columns and such. Theoretically, men are supposed to keep to the right and women, to the left, but in reality, nobody does it. People just mix together. But the left side (if you face the altar) is dedicated to the dead so there you'll find a large statue of Christ on the cross and a very special square candle stand with a cricifix over it, the only stand in the whole church to place candles for dead people. In front, there's the altar area that a female can't enter but male churchgoers can on certain occasions.
In the far right corner (if you face the altar) there's a booth where a special person stands who reads Psalms and certain prayers during the service. He or (usually) she has a lectern and usually a book case where she keeps all the books she needs and sometimes also sheet music.The choir loft is usually placed over the entrance, i.e. behind the worshippers' backs. If it's a small service, a group of two or three singers will place themselves in that booth and will sing from there using the sheet music in the book case. All singing is always live -- tapes are never used -- and usually very professional. Microphones are never used even in the biggest (read: gynormous) churches because the acoustics is so good you don't need amplifiers.
There're no special confession booths in the Russian Orthodox church. They did exist before the Second World War, but during the war, churches were so crowded with worshippers wishing to confess that booths were discontinued and instead, a confessor listens to people's confessions in full view: usually, they queue in the far left corner of the church by the altar and the person who confesses just steps a few steps away from the rest so they can't hear him. Confessions only take place just before the lithurgy (which in most bigger churches can be held on most weekdays, not just on Sundays) or the night just before. No one confesses at other times -- but they probably can if they arrange it personally with a priest.
BTW, nobody can turn their backs to the altar in the church! If you have to turn, you still need to remain sort of sideways to it :-)) Some of the more avid church goers and especially those order-keeping baboushkas will comment on it negatively :-((
As for the rest, the architecture varies greatly. There're churches with and without windows, with and without domes, some so tiny only a dozen people can fit in, others good enough for a thousand.