(I'm with Vector, the company behind CartThrob).
How familiar are you with you the basic ExpressionEngine table setup? CartThrob uses standard ExpressionEngine entries to store orders and member data, so familiarity with that would help.
All orders are stored as new rows in
exp_channel_data. This has the same setup as any other ExpressionEngine entry-- metadata about the order is in
_titles while specific custom field data is in
exp_channel_titles.author_id is the
member_id of the user that placed the order. The order ID/number is the
entry_id, which is the primary key on both tables.
If you have an order from
_titles, you can grab the
author_id and look that up as the
exp_member_data, which are standard ExpressionEngine tables for storing member information.
And, with the order ID/
entry_id, you can also query
exp_cartthrob_order_items to see what specific products were ordered as part of the orders.
Let me know if you need any further information! And, feel free to let us know if we can be of more project-specific help.