Can i combine 2 devices to get more power for mining As An example lets say i have 2 USB Miners each one has 16 GH/s
can i combine these 2 to mine with 32 GH/s ?

And if yes pls tell me how.
Yes. To do this simply mine with both at the same time. A mining pool will never give out the same work twice. So mining with two 16 GH/s devices will be the same as one 32 GH/s device.

If you mine at the same mining pool with both then the pool will show you mining at 32 GH/s.