Good practice is to store information in the smallest possible format. This is normally achieved by storing "repeating information" in a table. Each row in the table is identified by a unique identity an "ID field"… For example you could have a table which stores customer information, it might store:- salutation; surname; first name; address; telephone number. Each row of "information" would have a unique ID. 

When you want to use this information somewhere else, let's say you want to provide the customer details for an orders table, in the orders table you only need one field to identify the customer. You store the ID from the customer table in this field. But that's not a very user friendly method because the user is never going to know which customer any particular number refers to. This is easily solved by using a combo-box as effectively a up look-up agent.

When you create your "Orders Form" based on your orders table, it will very likely create a text-box for the customer field. As suggested this text box will just display the number relating to the customer. However if you change this text box into a combo box, you can do this by right clicking on it, then selecting the third option in the list "Change To" now you have a combo box. It's always a good idea to follow a naming convention so immediately find the combo box name in the property sheet under the tab "Other" and prefix it with "cbo".

Also the Combo Box default name might not mean much, and may contain spaces. Remove the spaces and rename it something meaningful to your programming processes. Now whilst you've got the property sheet open, select the data tab, select the ellipsis (…) at the end of the "Row Source" property and you will be taken to the query building tool. Select a Table, in this case you want the Customers Table. Select the customer ID field and the customer name field so they appear next to each other in the query builder grid. You need a minimum of two Fields, the ID field and the customer name field. You may want other Fields, for instance you may have a Boolean field to flag a discontinued customer. Select this field and set the criteria option to "False". Now discontinued customers will not show in your results. You don't want to see the "Boolean field" in the combo-box so make sure the "Show" checkbox is unchecked.

Close the query builder Grid and re-open the property sheet for the combo-box as we've got just a couple more things to check/set-up. On the data tab make sure that the "bound column" property is set to 1 and "limit to list" is set to true (Yes)… Select the format tab and set the column count property to 2, and the column widths property add the Text "0, 2" … 

The "bound column" is the column where the data from the combo box will be taken and fed back into your orders table, and you want the customer ID which will be bound column 1, the first, the left most part of the SQL/Query, in this case the ID. The column width property of the Combo Box is a way of specifying what actually appears in the actual combo-box, is Visible, is what the user sees. In this case we have have query which returns two columns, the ID and the customer name. But we don't want to see the ID, we just want to see the customer name. To do this set the "column widths" to 0; 2 — This shows Nothing of the ID, but 2cm of the customer name. Some versions of MS Access will not show centimetres but inches so the figures might be slightly different for your version of MS Access.

There are several other properties you can change for a combobox, however these property's I have explain here are the basics and you will seldom find yourself changing anything else….