Under "Network -> Objects -> QoS Classes", you can create and modify the QoS limits.
To add a new class you need to add a device first. You can click the "Add Device" button at the bottom and you will be presented with a dialogue box.
Choose the Device you want to have the QoS applied on (eg. eth1), choose the ceiling (usually for the device set to the speed of the NIC - eg. a 10Mbps NIC would hve a ceiling 10000 Kbit/s) and for the purposes of the interface, set the Assured as the same value.
Once you have created a device, click on the device to highlight it (denoted with a blue triangle) and click "Add Class" at the bottom of the window.You can then decide how you want to split up your pipe. You may like to call it "Internet" and set the Ceiling and Assured rates to the same limit eg. If you have a 8Mbps ADSL1 link, you can set the Ceiling and Assured to 8000.
When you have done that, click on the Internet class (denoted by the blue circle) and click "Add Class" again.
This time call this class "Normal Internet Access" (without the quotation marks), and set the ceiling to 8000, and the assured rate to 7000. Then click OK.
Highlight the "Internet" class for a second time, and click "Add Class". This time name the class "Limited Internet Access" and set the ceiling to 2000, and you should find that the "assured" rate will only go up to 1000.
The reason for this is so that you cannot over commit your bandwidth. The group that you apply the "Limited Internet Access" QoS Class to, will be guaranteed 1Mbps use, and if there is more bandwidth available, they can use up to 2Mbps.
There should be no reason to change the Priority, however if you wish you can do so. The lower the number, the higher priority. EG. Priority 1 means we treat this traffic higher than priority 7 traffic. The Advanced checkbox allows you to control the burst, however it is safe to leave this off and let the system automatically work things out.