You have seen the data sheet - freely available.
Each device has a unique 64-bit address. Your code will need to establish the addresses by reading those from the device and then store/manage the temperatures from each.
You can place all devices on the same 'one-wire' bus.
Suggest you start with one device, get that reading and get your code to read the device address, then add another to start building up the array to your desired maximum.
Some of the techniques are discussed here as an example: http://www.picaxeforum.co.uk/showthread.php?11100-update-on-the-1-wire-bus-master-DS2482-x00-please
Using the simple READTEMP commands you can only connect 1 DS18B20 per IO pin.
If you are using an X1 or X2 part then you can use the 1-Wire commands with multiple devices connected to a single I/O pin.
In my thread posted some time ago about 1-wire networks there is example code and a lot of information about the 1-wire networks. http://www.picaxeforum.co.uk/showthread.php?15306-One-Wire-Devices-Networks
The I/O pin used must be capable of being both an input and outputs.
See PICAXE manual pages (about) 8 onwards for pin outs and functions.
