Ok, I think the above all of the replies are trying to tell you the same thing, but I can understand if the OP isn't understanding.

Avios is two things. It is the currency as used in your BAEC account. You can also have a separate Avios account which (and this is the bit your probably finding confusing) also uses Avios as currency (the posters above are calling it an avios.com account to differentiate it from a BAEC account). It is the Avios account not the BAEC account that it is asking for.

One person can have both a BAEC account and an Avios.com account and move Avios the currency between the two.

Unfortunately, it looks like you are ineligible for an Avios.com account as I am guessing from your username your in ?paris, unless you have a UK address you can register. I'm afraid the estore is only available on the later type of Avios account, not the BAEC one.