How to implement Process queue module ?

Hey Team ! I am currently developing an application which is related to online shopping. As a customer, clicks on the Buy button which calls the microflow to place the order. But In my case, If 1000 customers clicks on the buy button at the same time, I want to achieve the multi threading functionality which allows only one customer to place the order while remaining calls waiting for the first order completion microflow. So I decided to use Process queue module. But I don’t know how to configure the process queue in my application. Even, I have read the documentation of the module and configured the Queue overview page  in my custom module. After that, I changed the buy button call microflow from my ACT_PlaceOrder to AfterStartUp_InitialiseQueue microflow. But It does not work which I was expected. Can anyone share screenshot of the microflow which helps to understand clearly. I am doing this task nearly 2 days. I could not find the solution. Can anyone help me to fix this problem ? Thanks in advance !!
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