Short answer
Perpetual futures do not expire, so they need another mechanism to keep the contract from drifting too far away from spot. Funding rate is that mechanism: longs and shorts periodically pay each other depending on whether the perp is trading rich or cheap versus its reference market.
When the perp is persistently expensive, longs usually pay shorts. When it is persistently cheap, shorts usually pay longs. The payment itself is not the strategy. It is the market pressure signal wrapped around the strategy.