When you register a new account, DGS asks if you already have a Go rank from elsewhere. For example, that could be from another Go server, your local Go club or the Go Association of your country. You may enter that rank, and, based on that, you will get an initial DGS rating.
 
If you do not know how to enter your rating this should help:
How do I set my DGS rating?
 
Alternatively, you may wish to look at this table of rank comparisons and enter the DGS equivalent to the rank you have from elsewhere. You can use Dragon's rank converter to convert Go ranks or ratings known from other servers into the corresponding DGS rating.
 
When setting up a new account, if you do not know your playing strength DO NOT enter anything in the rating field until you try some of the recommendations for figuring out what it is. This normally cannot be changed after you enter it. You will have to wait for your rating to adjust as you play.