'On the ground' means 'the thing of concern'. This could be a building, place, corporation or company. The 'people on the ground' are the people directly involved in the situation. This phrase is often used to talk about people in news reports who are living in an area where something is happening. The 'people on the ground' are the real, ordinary people affected by something.

1. Even after the ceasefire was agreed, tensions in the country are still running high. Therefore, UN observers have been put in place to monitor the situation on the ground.
2. We are reporting from the disaster zone in order to talk to people who have been affected on the ground.

1. It's no good taking the manufacturer's word for what's happening with our order. I want someone from our office on the ground to give me first-hand progress reports.
2. David felt that the company needed to have people on the ground to assess the quality of the goods in person rather than relying on images online.