First, you need a bicycle. I prefer a folding one because it is easier to transport. You don’t need a bike rack for it. Most of the attachments for bicycling with your dog will adapt to most bicycles.
You will need a device to attach to the bicycle that provides an attachment point for your leash. Many people use a standard leash in their hand. This is truly a bad idea. It puts everyone in danger, even if you are an experienced bike rider. For under one hundred dollars there are devices that can accomplish this task safely. Then, if your dog gets distracted and pulls in the wrong direction, you have better control. My only real experience is with a Springer Bicycle Attachment. I have used many of them and they work great!!
Another necessity is a proper dog harness. The Springer includes one in the box. It is not a harness you will get much use from. It is sufficient for training your dog. Once you start clocking some miles you will need to get a comfortable and good quality one. I use a high quality padded Tracking Harness. This provides the dog with the comfort and weight distribution to safely run with the bicycle using a Springer or similar attachment.
These are the basics you need to get started. An affordable fun way to get interactive with your Dog!!