Imagine if you have designed a Access form that shows everything about a customers order on the screen. The customers ask you something and you know it will take a few minutes to sort out so you say "I will get back to you". Then another customer calls about a different order which you now have to search for. If you open the detail form for the second customer, it is likely the first order form will be closed and the new customers order details will replace the other customers information. This is annoying at best.
Here is how you solve this, open the form as a form class instance. I discuss this technique in pdf article here. To find the relevant text, you will need to go down to the page that starts with "Open the same form twice". There are a few tricky things involved in this topic but you are a good Access developer, its good dependable gear.
In the following image you will see the same form opened 3 times for 3 different warranty claims. In this case the application is running in Tabbed Document mode.