Q. 1. What is the purpose of the lectern?
A. 1. According to the General Instruction of the Roman Missal (GIRM), it specifies:
# 260. The readings should whenever possible be proclaimed from the ambo or a lectern.
From the above, it is concluded:
The ambo is stationary and was designed for the minister of the word only. This is where the priest reads the Gospel and does the preaching.
The lectern is movable and intended for the readings other than the Gospel.
The pulpit, another term that is used, is not a Catholic word.
The ambo is still the official Catholic term for the place where the Gospel is read. The word ambo comes from a Greek word meaning both. This is to symbolize the readings from both, the ambo and the lectern. In common speach, ambos are incorrectly called pulpits, a Protestant word. There are no pulpits in the Catholic Church.
To answer your question, the lectern is where the Epistle is normally read, on the right side when facing the Altar. It is also used for the "Prayer of the Faithful," by the choir master, and other readings by laypersons.
The ambo is on the left side in the front of the Church. That is where the priest reads the Gospel and does his preaching.