You can not become a scientist if you require that every question has an answer because its the very questions that have no answer that attract you to a laboratory every single day.
Angel, first make sure you understand setting up proper tables and relationships, which I cover in Access 201 and 202. Then, you need to understand a three-way relationship with something called a JUNCTION table (or cross-reference table). This is how you can have two separate lists of things bound together by a third column. This is a little more advanced, and I cover it in Access 309.
For example, you would have a CustomerT table, with information like CustomerID, name, address, phone, etc. You would have a StockT table with your StockID, current price, volume, etc.
Now, you'd set up a junction table that has CustomerID, StockID, and any other information about the transaction between the other:
ID (Autonumber) CustomerID StockID PurchaseDate Notes
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