The specs actually say the Inspiron 3268 has a PCIe x16 slot for a video card, and Dell sold the Inspiron 3268 with an NVIDIA GeForce GT710LP (Low Profile), a single-width card.  This model has only a 240W power supply, so that limits your choices of video card. If you don't have any add-in video card now, you may want to get a GT710LP.  And unfortunately, the PSU in this PC can't be upgraded to accommodate a video card that requires higher wattage.
I have an inspiron 3268 with 180w psu. which graphic card can be used with it. thanks
INSPIRON 3268, WHICH GRAPHIC CARD IT SUPPORTS