Hi Tia,
Welcome to the Vodafone eForum from all of the team.
You don’t need to apologise as I know it can be a bit of a maze to find information on here sometimes. 
Please find the answers to your questions below;
The data allowance when in the UK ?
The data allowance on your contract (Internet Bundle) does vary from account to account however unless otherwise stated on your bill you should get 500MB of data each month to use whilst you are in the UK.
The data allowance and additional cost for use when abroad (say France) ?
At the moment it sounds like you don’t have any international data for use whilst you are abroad on your account and as such the charges would be those found here on our help centre.
However, if you are a frequent visitor to European countries then you would benefit from adding the Vodafone Data Traveller Monthly pack to your account.
Whether either of the above allowances are affected if the Blackberry is "tethered" to a PC ?
As you have a blackberry handset, the data in your price plan can also be used for tethering your handset to your PC.
As tethering can sometimes use a lot more data, the following charges would apply if you were to go over your 500MB bundle.
If you were intending on tethering your device then I would recommend looking at our tethering packs, more information about tethering can be found on our tethering support page.
If you have any other queries please let me know.
Also, if you have any comments on how I have answered your query today, please complete our short feedback survey.
James
eForum Team
