The Gigabyte AB350-Gaming 3 comes with one PCI Express 3.0 x16 slot, two PCI Express 2.0 x16 slots (one of them working at x4 maximum speed, and the other one working at x1 only) and two PCI Express 2.0 x1 slots.
The PCI Express 2.0 x16 slot that works at x4 speed shares its lanes with the PCI Express 2.0 x1 slots. So, it they are in use, this slot will work at x2 speed.
The motherboard supports CrossFire with up to two video cards, but it does not support SLI.
There is also one M.2 slot, supporting both PCI Express 3.0 x4 and SATA-600 SSDs.
The first two PCI Express x16 slots are covered by stainless steel shields, that work as a shield against interference, and also improving mechanical strength of each slot.
Figure 2: slots