The imam stands in front, in the middle of the row.
The should not be a gap of more than 2 rows between the imam and the followers.
If there is zahmah (severe crowd) then the followers can stand in line with the imam but should make sure that they don't stand in front of him.
(source:noorul idhah, quduri)
The Imam leads the congregation in prayer and delivers the khutbah or sermon, thus he stands in the front of the prayer hall so he is visible and can be heard by all.
Infront of everyone else.
The Ma'moomeen (The ones who are being lead by an Imam) stand behind him in prayer
In the front of everyone else
Imam
Currently Imam Khamenei is the leader of Shia Muslims.
An Imam.
shia Muslims
in Shia Islam Imam Khomeini and today Imam Khamenei
Shia just means the followers of imam ali ibn abu talib (as)
An imam is the man who leads prayers in a mosque. His office is where does his work, such as writing sermons.
The Imam
Most of the Jaafries are Sia. They calim to follow the teachings of Hazrat Imam Jaafar Sadiq RA. Yet, the Sunni Muslims also respect Hazrat Imam Jaffar Sadiq RA.
prophet Muhammad (PBUH) after him Imam Ali (sa) after him Imam Hasan (sa) after him Imam Hssain (sa) and then 8 Imam from children of Imam Hasan (sa) totally 12 Imam. currently Imam Mahdi who is dissappeared but some especial Shia Muslims meet him and he guids them. recently Imam Khomeini was leader of Iran Islamic revolution who was main shia leader in world. and after his death recently now Imam Khamenei is leader of Shia Islam in Iran and also shia countries. other local shia leaders exist in shia countries but Imam Khamanei is main leader in shia world.
Using it is not obligatoy. but shia use it mostly after dua.
To lead prayers and educate the followers of the teachings in the Koran