How two punishments awarded by courts to the same person be implemented at the same time?

This is a doubt and question regarding legal matters. No legal advice is necessary. Just a clarification.. A Mumbai court in INDIA gave 2 punishments to one person ( 1.Life imprisonment for murder and 2. Five years imprisonment for a grave offence) The court directed that the 2 punishments be implemented same time. My doubt is when he is undergoing life imprisonment, how the 5 years imprisonment can be implemented? When it can not be implemented what is the rationale in awarding a second punishment. Any legal experts are welcome to clarify this doubt. Thank you.