Column name or number of supplied values does not match table

Firstly check to make sure that the table has only the 4 columns that you have provided, if not then specify them by

SqlCommand cmd = new SqlCOmmand("insert into Order_Tb (Columnname1, Columnname2, Columnname3, Columnname4) values ('"+TxtDescription.Text+"','"+DdlWeek.Text+"','"+Ddlmonth.Text+"','"+DropDownList4.Text+"')",con);

But make sure that you replace Columnname1, Columnname2 etc with the actual column names from the table.

ALSO it is best practise not to concatenate strings together as this will open you to SQL Injection. Have a look at SQL Parameters, simple example in the following link.
http://www.dotnetperls.com/sqlparameter[^]

The error clearly says that You are not providing all the columns needed in table. If you want to insert some columns only you need to define those column explicitly.

Eg.

SqlCommand cmd=new SqlCommand("insert into Order_TB (Column1, Column2, Column3, Column4)values('"+TxtDescription.Text+"','"+DdlWeek.Text+"','"+Ddlmonth.Text+"','"+DropDownList4.Text+"')",con);
cmd.ExecuteNonQuery();
con.Close();

And one very important thing. You should never pass your text box or any other value to the insert script directly in code. It just opens door for sql injection. Alwaysuse sql parameter.

SqlParameter Class (System.Data.SqlClient)[^]

Never use concatenated strings to create your SQL command.

Use parameterised queries. Not only will that help to protect you from SQL Injection attacks, it makes it easier to construct the queries and helps to avoid some errors.

For example:

SqlCommand cmd=new SqlCommand("insert into Order_TB values(@Description,@Week,@month, @List4)",con);
 cmd.Parameters.AddWithValue("@Description", TxtDescription.Text);
 cmd.Parameters.AddWithValue("@Week", DdlWeek.Text);
 cmd.Parameters.AddWithValue("@month", Ddlmonth.Text);
 cmd.Parameters.AddWithValue("@List4", DropDownList4.Text);
 cmd.ExecuteNonQuery();
 con.Close(); 

Now look at your database table. What columns does it have ... Description, Week, month, List4 and nothing else (other than possibly an IDENTITY column).

If there are more columns on the table than that, then you need to do one of two things.

1. Give a list of the columns which you are going to provide. E.g.

SqlCommand cmd=new SqlCommand("insert into Order_TB (Description, Week, Month, List4) values(@Description,@Week,@month, @List4)",con);

(Note I have just guessed the column names - use your actual column names not the ones I have put in here)

2. Provide values for all of the columns in the table

SqlCommand cmd=new SqlCommand("insert into Order_TB values(@Description,@Week,@month, @List4, @column5, @column6)",con);

... etc