Like Bytes32, ContractId is a wrapper on [u8; 32] with similar methods and implements the same traits (see fuel-types documentation).

These are the main ways of creating a ContractId:

        use std::str::FromStr;

        use fuels::types::ContractId;

        // Zeroed Bytes32
        let contract_id = ContractId::zeroed();

        // Grab the inner `[u8; 32]` from
        // `Bytes32` by dereferencing (i.e. `*`) it.
        assert_eq!([0u8; 32], *contract_id);

        // From a `[u8; 32]`.
        let my_slice = [1u8; 32];
        let contract_id = ContractId::new(my_slice);
        assert_eq!([1u8; 32], *contract_id);

        // From a string.
        let hex_str = "0x0000000000000000000000000000000000000000000000000000000000000000";
        let contract_id = ContractId::from_str(hex_str)?;
        assert_eq!([0u8; 32], *contract_id);