Classes of comfort
Standard intercity trains are relatively comfortable all-sleeper overnight expresses. These have three main classes.
The best is 'SV' (pronounced 'ess-vay', translated as sleeping carrage) in which a special closable compartment holds just two passengers in relative luxury. These carrages are normally very clean (except the separate toilets) and you have your own reading light, fold out mirror and (for the better lower bunk) a small desk with a power-point. Roughly half the price are the most popular Kupe berths which have four beds in a larger, sparser compartment. Not available on all trains, the open Platskart class squeezes in a further two people by removing the compartment dividers and adding two berths along the walkway/corridor. These open carrages are clearly less secure than closed kupe compartments but many people use them across country without incidents. The corridor berths are short and best avoided.
If the train is almost full (most unlikely) and you're desperate to get aboard you might be able to get an 'obshchiy or umumi' (unreserved) ticket or go directly to the provodnik on the train itself and pay your way aboard. In reality the trains are rarely entirely full and there's often a small gaggle of locals trying to pay their way onto each carrage in the hope of saving a few manats over the full ticket pnce. This could be a dangerous tactic as you'll pay almost the same price without any guarantee of a place to sleep.
If you have luggage it can be stowed in a large box beneath the lower seats. Thus, for security, it is reassuring to have an (odd-numbered), lower ('ashagi' in Azeri) berth and act as sleeping guardian. In platskart or kupe the best berths are probably #17, #19 or #21 as they're in the middle of the carrage, well away from the smelly toilets. Avoid berth numbers over #33 in platskart since they are shorter, have no luggage box and, being alongside the passageway, are prone to frequent disturbance by other passengers wandering by.
There's a mattress roll and pillow to add comfort to each berth. Before you use these, however, you're supposed to fetch a set of clean, rented sheets from the provodnik and make up the bed properly. Depending on the fare you paid, the cost of sheet rental may or may not be included (it is usually included in tickets purchased ex-Baku). Ask the person at the ticket window to confirm this to avoid an unnecessary quarrel with the provodnik once aboard.
In Georgia, sheet rental is usually extra, the sheets if available come ironed and sealed in plastic bags, or you can use your own sleeping bag