Having read the instruction manual for this oven, it is far from clear what they mean by the different modes. However, there are some clues and the generic design of most modern appliances should apply here.
Modern electric ovens comprise of 3 heating elements, 2 flat zig-zag elements and a circular fan element. One in at the top of the oven, one is in the bottom, and the fan element is at the back.
When in convection mode, this fan will be running, but may or may not be in conjunction with the circular element. This allows food to be cooked via the top element only with rapid air circulation facilitated when the door is closed. Alternatively, the top element only can be used with the fan off, in which case the door should be left open.
In standard convection mode, the circular element and the fan will be running, and the upper and lower elements turned off. This equates to a standard fan oven, roughly 10% hotter than a non-fan electric oven.
The top and bottom elements can operate independently, allowing heat to come from the top, bottom, or both directions simultaneously. Some ovens may allow the fan to be used (and its corresponding heating element) simultaneously. So to summarise, the modes we have are as follows:
- Top element only
- Top element with fan
- Bottom element only
- Bottom element with fan
- Top and bottom element no fan
- Rear circular element with fan
- Top, bottom and circular elements with fan
These equate to the difference roasting and baking modes on your model I presume, my cooker is more explicit in stating they are for pizza, cakes and bread etc.
If you have a digital thermometer, I would try out each of the modes and plotting the temperatures to see what equates to what.
Obviously, there will be differences between models, for instance my oven has a defrost function which is a very low heat setting. What element it uses I know not, but as previously mentioned, a lot of ovens have functions most of us will never use.