Go to Market Place section of this website.
Click on the category you are interested in buying from. Narrow down your search by clicking on your location of interest. If no location is chosen, ads from your selected category will appear from all locations.
Click on ads to survey them. If interested, contact the seller either by sending them a "Chat" message on their NkB Market Place account, or by contacting them with any of their displayed contacts; either by phone or by email.
It is always safer to contact them first by sending them a "Chat" message on their NkB Market Place account. Make enquiries about any details. Confirm the details and price are as stated on the ad. If you both reach a deal, arrange where to meet. Meet in an open place. See product before you pay.
For further safety tips, read Stay Safe Online to know how best you can go about with your transactions in the safest possible ways.