The slot: What is it and how can I use it?

Which Slot to use? what is an m 2 slot Two types of SSD Note: SSDs using the PCIe x4 bus use M-keys since it is the only one that supports PCIe x4 lanes what is a slot fish M 2 is a slot that can interface with SATA , PCI Express

what is the best slot machine to play 2 slots, which will be PCIe X4 Gen 34