//create strings
string connStr = "--snip--";
string cmdStr = "select field1, field2 from table1 where field3 = @field3";
//create objects
SqlConnection conn = new SqlConnection(connStr);
SqlCommand cmd = new SqlCommand(cmdStr, conn);
//add parameters
cmd.Parameters.AddWithValue("@field3", "someValue");
//open and execute
try {
    conn.Open();
    cmd.ExecuteNonQuery();
}
//handle SqlExceptions
catch (SqlException ex) {
    //handle Exceptions
}
//handle generic exceptions
catch (Exception ex) {
    //handle exceptions
}
//no matter what, make sure the connection is closed
finally {
    if (conn.State != ConnectionState.Closed)
        conn.Close();
}