LSC elections are held in the spring of even years. The next elections will be in 2018.
All LSCs consist of 6 parent representatives, 2 community representatives, 2 teacher representative, 1 non-teaching staff representative, and the principal. High school LSCs also have 1 student representative.
For neighborhood schools, parents of current students, and any adults 18 or older who live in the primary attendance footprint of the school, are eligible to vote for parent and community representatives. Note that non-citizens are eligible to vote in LSC elections! For some non-neighborhood schools, only parents are eligible to vote since there is no primary attendance footprint; but for others, there is still an attendance footprint.
This extremely helpful site can tell you, based on your address, which school elections you can participate in based on the school footprint.
There is also a separate election held on the same day for the teacher and staff representatives. Only teachers and staff can vote in that. Teachers and staff do not vote for parent and community reps, unless they themselves happen to be parents or residents within the footprint.
There is no early voting available. All elections take place at the schools themselves.
More detailed information is available on the CPS website.