BI Aggregates and BI Accelerator

Hi All

BI Aggregation is used to improve Query Performance. I have created an aggregation by using system "generated proposals"

If we want, we can create an aggregation on any field.....

can you please give me few tips how to select a field for an aggregation...

I am not getting BI Accelerator option when i select cube....for that what we have to do?

I read some where we can not use BI Accelerator along with BI Aggregators.... if so, why not?

Regards,

Vijay