...
hg clone https://bitbucket.org/ryzom/ryzomcore
Later, to update sources you will need to type :
...
With TortoiseHg, you will need to click right on your new empty folder and click on "TortoiseHg -> Clone" and you will get this dialog :
Source path: will be https://bitbucket.org/ryzom/ryzomryzomcore
Destination path: will be the folder where you want put all sources.
read write access with specific username
hg clone https://USERNAME@bitbucket.org/ryzom/ryzomryzomcore
USERNAME is your login on BitBucket.