I am new in mining DG Coin, and register in the the blocksfactory, can anyone let me know how to start mining?

You will need an SHA256 Algorithm miner.

1. You need to register at https://dgb-sha.theblocksfactory.com/
2. Input the stratum url stratum.dgb.theblocksfactory.com:9001, yourworkername and workerpassword into your SHA256 miner.
3. Start mining

You need a miner that will mine the correct DGB Algorithm for the DGB pool you are mining at. Normally you can find this info in your pools "Getting Started" page. Here are some examples:

Algorithm
-----
DGB Groestl https://dgb-groestl.theblocksfactory.com/gettingstarted
DGB Qubit https://dgb-qubit.theblocksfactory.com/gettingstarted
DGB Scrypt YOU NEED A SCRYPT ASIC MINING DEVICE
DGB sha256d YOU NEED A SHA256 ASIC MINING DEVICE
DGB Skein https://dgb-skein.theblocksfactory.com/gettingstarted

Here is the official bitcointalk thread: https://bitcointalk.org/index.php?topic=408268.0

Enjoy!