What is the role of organelles in the cell?

There are lots of definition we can use.

An organelle is a subcellular structure that has one or more specific jobs to perform in the cell, much like an organ does in the body.  (National Human Genome Research Institute. USA)

Cytoplasmic organelles are "little organs" that are suspended in the cytoplasm of the cell. Each type of organelle has a definite structure and a specific role in the function of the cell. (National Cancer Institute)

"Membrane-bound organelles such as mitochondria, peroxisomes, or the endoplasmic reticulum (ER) create distinct environments to promote specific cellular tasks such as ATP production, lipid breakdown, or protein export. During recent years, it has become evident that organelles are integrated into cellular networks regulating metabolism, intracellular signaling, cellular maintenance, cell fate decision, and pathogen defence." (Schrader et al. T_he different facets of organelle interplay—an overview of organelle interactions. _Front. Cell Dev. Biol., 25 September 2015 | https://doi.org/10.3389/fcell.2015.00056)