What is The function for converting a string To google protobuf format?

I want to convert a string to google protocol buffer format. like this format below:

message employee
{
    required string first_name = 1;
    required string last_name = 2;
    required string email = 3;
}

message Company
{
    required string name = 1;
    optional string email = 2;
    repeated Employee employee = 3;
}

But i don't know the function of google protobuf that get the string to decrypt it. please give me a example that get a string and return the google protocol buffer format. Thank you!