First, let us look at the definitions. Energy is the capacity of doing work while work happens when any system or device uses that energy stored in it. Both quantities have the same unit. The main difference here is that work or work done is the process of converting the energy of one system (device) into another system.

For example, consider a man ready to lift a stone from the ground. The man has chemical energy stored in his body which he got from foods. The stone lying in the ground has no energy (potential energy). Once the man lifts the stone to a certain height, the stone acquires potential energy while the man just transferred chemical energy (of the high body) to potential energy (of the stone). So, this process is known as work done.

This is also the reason why both energy and work done is measured with the same unit. Because both represent energy. Work done only represents the energy being transferred.