string

string is first converted into its bytes type by converting each individual ASCII character to its hexadecimal value. It is then stored in the exact way bytes are stored.

Example, a string type, "hello" would be first converted into 0x68656c6c6f, a concatenation of each hexadecimal value of each character, and then stored just the way bytes are stored.

To get a knowledge of what the hexadecimal values of ASCII characters are, you can look up this table at RapidTables.com.

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;

contract Yul {
    function stringInMemory(string memory value) public pure returns (bytes32) {
        assembly {
            let valueLoc := add(value, 0x20)
            let bytesValue := mload(valueLoc)
            mstore(0x80, bytesValue)
            return(0x80, 0x20)
        }
    }
}

Refer to bytes.