Resources and guide on bridging.

What does Bridging mean?

A bridge is a connection between networks that enables the transfer of tokens or arbitrary data from one network to another. For the most part, users bridge their funds from Ethereum to a "layer 2 solution".

What's a Layer 2 Solution?

A layer 2 solution is a network built on top of Ethereum that enables users to experience faster transactions with cheaper gas fees without giving up decentralization and security.

List of Bridging Websites

Note: Bridging FROM the Arbitrum, Optimism, or Polygon networks is takes some time. In some cases it may take up to over 2 weeks for your funds to appear on Layer 1 (Ethereum Network). A solution to this would be using non native bridges like Anyswap or Hop. Depending on network usage, it is sometimes even cheaper to use these protocols over the native network bridges.

Do these networks use ETH as gas for transactions?

Arbitrum and Optimism yes.
Avalanche uses its native token AVAX. You're automatically airdropped some into your wallet when you bridge over $75 of crypto using their native bridge.
Fantom uses its native token FTM. To receive some FTM use the following guide created by Mentasuave​
Polygon/Matic uses its native token MATIC. You're automatically airdropped some when you bridge funds using their native bridge.

Manually Add Networks

In the case that the network you're bridging to is not automatically added to your Metamask you can use Chainlist to add it manually.
Chainlist is a list of EVM networks. Users can use the information to connect their wallets and Web3 middleware providers to the appropriate Chain ID and Network ID to connect to the correct chain.