Instantiating a Contract Class requires two steps. First, import the Contract you need from the SDK. Imports are explicit; read through the protocol architecture docs or the repo to understand which contract (or contracts) you will need.
Next, instantiate a new class by passing it two parameters:
The address at which the contract is located on chain. Vault-specific contract addresses are available on the Vault's overview page on the Enzyme app. Non vault-specific contract addresses can be found here.
A Signer object. A Signer is a class imported from ethers and instantiated per their documentation. It describes the user on whose behalf the contract is being instantiated (and who will eventually call any methods on the class) and a connection to an Ethereum node.