Can I use two different types of Ram?

The two sets I have are..

G.SKILL Value 8GB 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-1600C11S-8GNT

(2x for 8gb) Corsair XMS3 4 GB 1333MHz PC3-10666 240-pin DDR3 Memory Kit for Core i3 i5 i7 and CMX4GX3M1A1333C9

I heard that the 1333MHz can overclock to 1600...but I dont know much so help please.

Thank you

As long as all DIMMs are DDR3, you can mix and match. What happens (by default) is all DIMM's accommodate the lowest common denominator. In other words, they will only be as fast as your slowest stick. You can manually overclock the slower stick, but that's definitely something for more advanced overclockers. I don't even bother with RAM overclocking.

YES!!!!!!!   but one type will be made slower to accomadate the lower speed (G SKILL) 1600mhz 

you can just make sure your mother board to see what maxium Mhz it support if it lower than your RAM invest in a cheapper RAM or a new motherboard

As stated above when it's all installed it will default to 1333mhz or 667 depending if it's showing you the total memory speed or speed of each individual channel. Depends a lot on your motherboard how easy it is to overclock of if it's even supported as some boards will not let you change the timings or voltage manually.