What is an slot on a motherboard used for?

m slot  Buy B + M Key slot to 4 Port SATA 6G Adapter controller Card Support win 8 10 at Aliexpress for Find more , and products  Utilize an available PCIe x4 expansion slot for the installation, removal, or interchange of PCIe SSDs The drive tray accommodates M-Key NVMe SSDs

I'm trying to figure out what type of SSD my motherboard supports but the owner manual just says 22x80 socket3, does it support NVMe Hi, We wish to get an additional PCIe slot out of our AGX Xavier Developer Kit, and so purchased an to PCIe adapter ( NVMe to PCIe

Buy B + M Key slot to 4 Port SATA 6G Adapter controller Card Support win 8 10 at Aliexpress for Find more , and products  Locate the PCIe slot This slot is usually easy to find in desktops, but in laptops the location will vary