How do I send strings of data to a SQL query? [closed]

I would highly recommend NOT to store passwords as plain text. Instead look into hashed password methods.

Firstly you will need to specify a connection string. This can be done in the config file as:

<connectionStrings>
<add name="myConnectionString" connectionString="server=ServerAddress;database=myDb;uid=myUser;password=myPass;" />
</connectionStrings>

Now you want to read the connection string from your config file and you can do that in your C# code as:

string connectionString = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;

I'm assuming you'll be inserting records. If you are going to update records, then you will need to change the query. For inserting records:

string myQuery = "INSERT INTO MyTable (UserNameColumn,PasswordColumn) VALUES (@UserName, @Password)";

Finally to execute the query and pass our parameters we can do

using (SqlConnection connection = new SqlConnection(connectionString))
{
   using (SqlCommand cmd = new SqlCommand(myQuery, connection))
   {
     cmd.Parameters.Add("@UserName", SqlDbType.NVarChar).Value = UserNameTextBox.Text;
     cmd.Parameters.Add("@Password", SqlDbType.NVarChar).Value = PasswordTextBox.Text;

     connection.Open();
     cmd.ExecuteNonQuery();
   }
}

Dont forget to include the namespace using System.Configuration;