A lector is someone who participates in the mass by proclaiming the first and/or second reading and if no deacon is present the prayers of the faithful.
They announce all hymns for the mass as well unless the choir direction does this at the parish you are reading for.
You read approximately once a month at a preschedule mass, volunteers can switch with one another if the date they are assigned does not work for them
A good lector prepares by practicing the readings ahead of time. This helps with understanding what is being read and how to pronounce the words, creating a fluid, calm, deliberate delivery with clear pronunciation and unreushed speaking. The ability to read slowly and clearly with appropriate expressiveness that is not too dramatic is desired.