Does anybody know how exactly to connect to Terraminer machine via USB?
First of all, did you read the manual?
This is a miner with a mining controller on board, specifically the beaglebone black. This allows the miner to do 'standalone mining', meaning it does not need a computer to control it, it has it's own microcontroller to connect to a pool and get the necessary information to start hashing away.
If you do want to connect the miner to a computer:
Accessing the TerraMiner via Serial Port You can access the TerraMiner by connecting a USB cable between a computer and the TerraMiner’s serial port and using a terminal program. The login is root and the password is cointerra.
But the manufacturer does say:
NOTE: Accessing the TerraMiner through the serial port is unsupported by CoinTerra. The Technical Support team will not be able to answer any inquiries regarding serial port access. Accessing the TerraMiner via the serial port and modifying the software will invalidate the product warranty.
Edit after comment:
I do not own this machine myself, so I can't say this out of experience. But from what I can read, the miner has a Beaglebone board inside of it, as the miner controller. A beagle bone has a micro USB connection, so plugging in a USB cable into the Beaglebone would allow you to connect to it.