Quarians are similar to humans in their appearance although they are a little shorter and lighter. They all wear life support suits, a necessity due to their compromised immune system that was a result of them living in the sterile environments of their ships.
The Quarians are a nomadic species. They live in a fleet of ships called the Flotilla (also referred to as the Migrant Fleet), although this was not always the case. They initially used on to live on their own homeworld, but were driven out by the Geth, a race of artificially intelligent machines that the Quarians had created almost 300 years before the start of the first Mass Effect game. They were made in order to make the lives of the Quarians easier but they kept adding functions to them until they accidentally became sentient and gained artificial intelligence. AI is restricted by the council due to the dangers that it possesses to the rest of the galaxy. Thus, upon learning their mistake the Quarians tried to the destroy the Geth who rebelled against them and forced them to leave their homeworld.
Quarians have strict social and political guidelines. The flotilla does not allow for a lot of space and resources are limited. Thus, each Quarian family is only allowed one child to assist in population control. When a Quarian child grows old enough they are sent on a journey called 'The Pilgrimage'. This pilgrimage must be done alone and the ultimate goal is to bring back something of value that can be used by the Migrant Fleet. The purpose was allow the young Quarian to prove their worth to the greater Quarian society as well bringing new resources to the Flotilla. The Quarian ends the pilgrimage by bringing back a gift and presenting it to the captain of a ship within the Flotilla, different from the ship they were born on. The captain accepts the gift if it is worthy and would take the Quarian on his own ship where they would live and serve.
Quarians used to have an embassy at the Citadel but were removed after they created the Geth, seen as irresponsible stewards of advanced technology. They are still viewed suspiciously by other races in Citadel Space. Their own government includes of the Conclave and the Admiralty board. The Conclave represent the civilian government, while the Admiralty is part of the military government and consists of the five highest ranking offices in the fleet. Each captain has full authority on his ship to make his own decisions but is also advised by a member of the Conclave. The Admiralty Board has absolute power in times of emergencies to veto any decision made by the Conclave. This can only be done once by each individual Board, since each Board member must resign after they make the decision and only if all of the five are in agreement to veto. Thus this prevents any abuse of power by Admiralty Board.
Quarians are also known for their skill at technological improvisation. Due to the ongoing nomadic state of the Flotilla, individual ships of the Migrant Fleet must function on pieces of hardware they are offered on various planets that Quarians visit. The Quarians' poor social standing and public persona as social pariahs make it difficult to get high-grade materials at decent prices. They thus are forced to compromise with what they can find, often discarded, outmoded technology. Each Flotilla ship is a collection of cast off material from literally dozens of different planets, a collection of junk loosely held together. Because of this, most Quarians have a fairly extensive knowledge of mechanics and engineering.
Quarian names are usually made up of three components. The first part is the given name, the second is the clan name, while the last part is a ship's name. Before their pilgrimage--a coming-of-age ritual--Quarians live on the ship they were born on. Therefore, they carry the name of their birth ship until they successfully complete their pilgrimage. After this ritual, the Quarian will serve on another ship which is reflected in their name. In Tali's case she was born as Tali'Zorah nar Rayya. "Tali" is her given name, "Zorah" is her clan name while "Rayya" is the name of her birth ship. In the grammatical structure of this name, "nar" is a modifier that signifies the fact that the Rayya is her birth ship. After her pilgrimage, Tali transferred to the Neema and thus became known as Tali'Zorah vas Neema. "Neema" is the name of the ship she serves on which is signified by the modifier "vas". In Mass Effect 2 Tali eventually rejoins Shepard's crew onboard the Normandy which, according to the tradition of the Quarian people, makes her Tali'Zorah vas Normandy.