What does PCIe-x16 really mean and how many do I need?

Types of PCIe Slots PCle Lanes pci e x16 slot It's a slot of x16 size but electrically x4 This pcie x1 in x16 slot I tried the clear CMOS procedure again and that didn't fix the issue I tried a GTX 750 ti(that uses the power of the slot and not external

pcie4 slot In ASUS 「PCIe x16 Slots - 7」