The general idea is Layer 2s solve high gas. Most users will be using apps that run on a layer 2 and will make rare trips to the mainnet. The next thing being worked on is onboarding users direct to layer 2, and layer2 interoperability so you can move from one l2 to another

You can already use an L2 DEX to exchange tokens (and have been able to for about a year) https://exchange.loopring.io/

You can send L2 payments with https://zksync.io/

But those are limited to their applications. General purpose L2s arrive this month! with Optimism https://optimismpbc.medium.com/ and to be followed later this year by https://aztec.network/ and others.

With those we can redeploy code from mainnet to layer 2. With the apps on layer 2 the transaction fees will be fractions of cents and almost instant and a lot of the programs we have dreamed about but not been able to make become possible at scale.

Its an exciting time!

I would recommend reading about ETH 2.0. There are a few aspects to it that increase scalability and drive down gas prices. Unless I'm mistaken proof of stake will contribute to this as the "work" is done away with.

Eth 2.0 has been slow and a long time coming, but it's the future and inevitable IMHO.