classes- getting their slowly but surely I think

just a quick query, hopefully someone can help (sorry for these repeat schooboy questions) re classes- Can you create an instance of a class and use its 'value' within an instance of another instance of the same class? For example I have created two classes- html.class and db.class I am creating an instance of the db.class to give an array containing the rows from a table. I would like to create a table using my HTML.class and using a while loop create a <tr> using the date collected from each row in my db.class. This all works fine. However when I embed this newly created table into a cell of another table created with html.class, the table is still created but it does not appear in the cell, but outside of the desired table- so I have two tables side by side instead of one table embedded within the cell of another? Is this a code/ syntax issue or have I misunderstood the scope of classes? Thanks