Ether (ETH) is the native token of the Ethereum blockchain and wrapped Ethereum (WETH) is a 1 to 1 representation of ETH but in an ERC-20 token format.
When you transform ETH into WETH, 1 WETH is worth 1 ETH because people may transform it back to ETH whenever they want.
Basically, you send ETH to an ERC-20 standard smart contract and it will send you back WETH to your same account. In the same way, when you send WETH to the ERC-20 smart contract it will send you back ETH to your same account. This is how the 1 to 1 convertibility is kept.
On Emerald you may transform ETH into WETH or back whenever you want. The function is inside your wallet under the symbol WETH, where it has a small circle arrow beside it to transform ETH into WETH or vice versa.
The process of transforming ETH into WETH is called wrapping. The function of transforming WETH back into ETH is called unwrapping.
What is WETH used for?
If you transform ETH into WETH inside the Ethereum blockchain, you may use it to operate with dapps. Dapps on Ethereum are usually compatible with ERC-20 tokens, so using WETH instead of ETH is convenient. Such dapps may be decentralized exchanges like Uniswap, which is used to trade ERC-20 tokens inside Ethereum, but cannot support ETH itself.
Another use case is to send ETH to a smart contract inside the Ethereum blockchain and to get WETH in other blockchains to use it inside those other networks. This is what is called "interoperability" as the native cryptocurrency of one blockchain may be used in another.