A quick check of your motherboard’s connectivity, and the size of the connector on your card, will make it obvious which slot is appropriate.
There are a few different types of PCIe slots. Many expansion cards use the “PCIe 4x” slot, which is much shorter than the full PCIe slot used by video cards. A quick check of your motherboard’s connectivity, and the size of the connector on your card, will make it obvious which slot is appropriate. If in doubt, refer to the expansion card’s manual.