Really, the differences between these two questions directly relates to your business individually. At the most general level, the target market is the customer subset that you are going to be marketing to, where as the customers section may differ in that these are the specific customers that are using your product now. Target market may be the market that you are going to targeting or feel is the best market for you company to be in the future.

Another example may be that the target market differs from customers in that the target market may be slightly more broad, and describe demographics where the customers can be more specific or focus on a single area.

Realize too that not every section needs to be completed. Some investor groups may require them to be answered, but others do not. You can also comment as you see fit in each section.

Does this help?

There doesn't necessarily need to be a difference between the two. They are very similar. For target market, I personally would use this to describe more of what my market is and customers as to who/why they are the market.

For example, if I would use Target market to describe my market technically, using demographics. I would explain the age group, the sex, geographic locations, etc. It could be expanded on if this is not enough. For customers, I would focus more on why this is the target. For example, I would say that I am targeting males ages 18-25 because of xyz.

Again, there doesn't necessarily need to be a difference, or at least a very large difference. Many times the information here would be estimates anyway if you are in early stages. I would still stick to describing the customer more detailed in the customer section and more technical or what your future plan is in the target market.