I'm unable to understand Lightning network properly

So I recently got to know about Lightning network so I gone through it and unable to understand how someone can get fiat after recieving micro-crypto from the network after depositing bitcoin to Lightning network. Will their be a price increase of bitcoin with adoption of Lightning network? So basically lightning network just act as a side chain but have same privacy and security as of bitcoin? What are the other drawbacks of the network and what are the main difference between lightning network and Drivechain? Just curious and open to learn more .