Hi, can anyone tell me how do I determine my need for a shopping cart?

The main determining factor is your number of products. If you have only one or two products to sell, you may be able to get by without any type of shopping cart, just a simple order form.
If you have a number of products arranged across a multi-page site, and want your customer to be able to browse your pages, picking items at will with the selections stored for check-out at one central screen, it would be a good idea to have some sort of “shopping cart.”