An ISA (Individual savings account) is for UK residents/tax payers only.
It allows you to deposit up to Ā£20,000 a year which is shielded from tax (including your capital gains - profits).
Depending where your from you may have a similar thing under a different name, for example in the USA they have a ROTH IRA (Individual retirement account).
I see, I will have to ask if that exists in Austria. I wont be able to save more than 20k a year anyway, so some tax relief would be great, I will look into that