please explain me why we using certain thing

public void InsertUpdateDeleteSQLString(string sqlstring)//here why we use string sqlstring.can please any one can explain me in detail regarding this.

        {

            SqlConnection objsqlconn = new SqlConnection(conn);

            objsqlconn.Open();

            SqlCommand objcmd = new SqlCommand(sqlstring, objsqlconn);

            objcmd.ExecuteNonQuery();

 

        }

 

        public object ExecuteSqlString(string sqlstring)

        {

            SqlConnection objsqlconn = new SqlConnection(conn);

            objsqlconn.Open();

            DataSet ds = new DataSet();

            SqlCommand objcmd = new SqlCommand(sqlstring, objsqlconn);//how this sqlstring works here please explain me .

            SqlDataAdapter objAdp = new SqlDataAdapter(objcmd);

            objAdp.Fill(ds);

            return ds;

        }