First of all many people wonder why Shias self flagellate every Moharrum.
The reason is that in 61 hijri after the martyrdom of Imam Hussain and the menfolk of his family including his 6 month old son there was oppression against them. They were denied kafans and burial. Their heads were cut off and impaled on spears to be taken to the royal court in  Damascus
The family of Imam Hussain( except for one sick male surviving member – Imam Zainul Abidin, only women and children)  was immediately imprisoned and made to march as prisoners to Damascus to the court of Yezid.
They were not allowed to weep their dead.
Today Shias compensate for that

Imambara : This is different from a mosque as prayers are not held here. Its used for gaTherings where the sacrifice of Imam Hussain is commemorated and talked about

Majlis : A congregation at an Imambara, which follows a fairly precise procedure, is called a #majlis

A #majlis follows a set pattern first
1. Sozkhani or the singing of marsiyas or elegies of unparalleled beauty set in classical raaga
The musical origin of #sozkhani was the Hindustani classical tradition of vocal music and its concept of ragas.
However, the singing was not accompanied by any instruments.
The elegies sung were poetic compositions devoted to the martyrdom of Hussain by some the finest poets that have lived in India &in Persia

2. Hadis :  this is divided in 2 parts
1) fazail – general discussion on points of religion
2)sacrifice of Imam Hussain and his family

3. Nauha : This is followed by nauha or elegies set to music ( no instruments)  which describe the martyrdom of Imam Hussain accompanied by matam

Matam : beating of chest in beat with the nauha. This is to express solidarity with the Sorrow of Imam Hussain’s family.

Alam : this is a symbol of Hazrat Abbas the commander in chief of Imam Hussain’s army. Its the army standard and he was the standard bearer.
He is also calked Abbas Alamdar

Zarih : every Imambara has this. Its a replica of the mausoleum of Imam Hussain Karbala. These are made of wood, brass, silver and gold and are permanently kept there

Taziya : These are again replicas of the mausoleum but are made of paper and bamboo and are buried on 10th Moharrum – ashoor