Definition - What does Associate Justice mean?
Associate justices are judges that work within a panel of judges; they are not at the top of the legal structure.
Normally, if a court only has one judge, then that judge would represent the top tier of the court. In appellate court, or where there are a group of judges working, the term "associate judge" refers to all all that are not the presiding (main) judge.
Justipedia explains Associate Justice
An associate judge has the same ability to determine and mete out sentencing, or rule over cases generally, that any judge has.
If the judge is part of a supreme or appellate court, the cases that they rule over would be of a different nature than those that normally go in front of a court. In this sense, the judges might all hear the same case and be asked for individual rulings that would be counted at the end for a score of how each judge voted.