Executing query with parameters

You could open yourself up to SQL injection attacks here, so best practice is to use parameters:

using (SqlConnection dbConn = new SqlConnection(connectionString))
{
    dbConn.Open();

    using (SqlTransaction dbTrans = dbConn.BeginTransaction())
    {
        try
        {
            using (SqlCommand dbCommand = new SqlCommand("insert into [DB].[dbo].[User] ( [Id], [AccountId], [FirstName], [LastName], [JobTitle], [PhoneNumber] ) values ( @id, @accountid, @firstname, @lastname, @jobtitle, @phonenumber );", dbConn))
            {
                dbCommand.Transaction = dbTrans;

                dbCommand.Parameters.Add("id", SqlType.VarChar).Value = id;
                dbCommand.Parameters.Add("accountid", SqlType.VarChar).Value = accountId;
                dbCommand.Parameters.Add("firstname", SqlType.VarChar).Value = firstName;
                dbCommand.Parameters.Add("lastname", SqlType.VarChar).Value = lastName;
                dbCommand.Parameters.Add("jobtitle", SqlType.VarChar).Value = jobTitle;
                dbCommand.Parameters.Add("phonenumber", SqlType.VarChar).Value = phoneNumber;

                dbCommand.ExecuteNonQuery();
            }

            dbTrans.Commit();
        }
        catch (SqlException)
        {
            dbTrans.Rollback();

            throw; // bubble up the exception and preserve the stack trace
        }
    }

    dbConn.Close();
}

This is a good article for beginners with ADO.Net

EDIT - Just as a bit of extra info, I've added a transaction to it so if the SQL command fails it will rollback.

    using SqlCommand cmd= conn.CreateCommand())
    {
                        cmd.CommandText = @"INSERT INTO TABLE (COLUMNS) VALUES (@Id, @account etc...


                        cmdUser.Parameters.Add(new SqlParameter("@User", SqlDbType.UniqueIdentifier) { Value = UserTypeID });
                        cmdUser.Parameters.Add(new SqlParameter("@Id", SqlDbType.UniqueIdentifier) { Value = ApprovalTypeID });
                        cmdUser.Parameters.Add(new SqlParameter("@AccountId", SqlDbType.UniqueIdentifier) { Value = UserID });
                        cmdUser.Parameters.Add(new SqlParameter("@FirstName", SqlDbType.NVarChar, 100) { Value = Name });
                        cmdUser.Parameters.Add(new SqlParameter("@JobTitle", SqlDbType.NVarChar, 100) { Value = Surname });
                        cmdUser.Parameters.Add(new SqlParameter("@PhoneNumber", SqlDbType.Bit) { Value = Active });
    cmdUser.ExecuteNonQuery();
}

        try
        {
            using (SqlConnection cn = new SqlConnection(this.ConnectionString))
            {
                SqlCommand cmd = new SqlCommand("Insert_User", cn);
                cmd.CommandType = CommandType.StoredProcedure;
                if (cn.State != ConnectionState.Open)
                    cn.Open();
                cmd.Parameters.Add("Id", SqlDbType.NVarChar).Value = "00A640BD-1A0D-499D-9155-BA2B626D7B68";
                cmd.Parameters.Add("AccountId", SqlDbType.NVarChar).Value = "DCBA241B-2B06-48D7-9AC1-6E277FBB1C2A";
                cmd.Parameters.Add("FirstName", SqlDbType.NVarChar).Value = "Mark";
                cmd.Parameters.Add("LastName", SqlDbType.NVarChar).Value = "Wahlberg";
                cmd.Parameters.Add("JobTitle", SqlDbType.NVarChar).Value = "Actor";
                cmd.Parameters.Add("PhoneNumber", SqlDbType.NVarChar).Value = "9889898989";

                return cmd.ExecuteNonQuery();
            }
        }
        catch (Exception ex)
        {
            throw new Exception(ex.Message);
        }

and for stored procedure, in sql:

    create procedure [Insert_User]
(
@id as nvarchar(100),
@accid as nvarchar(100),
@fname as nvarchar(100),
@lname as nvarchar(100),
@jobtitle as nvarchar(100),
@phone as nvarchar(100)
)
    INSERT INTO [DB].[dbo].[User]
               ([Id]
               ,[AccountId]
               ,[FirstName]
               ,[LastName]
               ,[JobTitle]
               ,[PhoneNumber]
              )
         VALUES
               (@id
               ,@accid
               ,@fname
               ,@lname
               ,@jobtitle
               ,@phone])

also, you can use text boxes or other input type controls to set values. You can change dataType, as you wish, such as uniqueidentifier, int, etc. If one or more of values are set as identifire, eg. AccountID, remove them from query.

Frankly, ADO.NET makes it hard to do things like this correctly. Tools like Dapper exist to make that easier:

dbConn.Execute(
     @"insert into [DB].[dbo].[User] ( [Id], [AccountId], [FirstName], [LastName],
                                       [JobTitle], [PhoneNumber] )
       values ( @id, @accountId, @firstName, @lastName, @jobTitle, @phoneNumber )",
       new { id, accountId, firstName, lastName, jobTitle, phoneNumber });

This will deal with all the parameterization for you, efficiently, effectively, and safely.

There are similar APIs for executing queries and populating objects.