Doubt about purschasing Bitcoins at Bisq

I am new in this kind of Platform and I would like to know, if there is an offer amount can we purchase part of the offer amount or only the whole offer amount ?

Yes you can, but only if the offer specifies that you can buy within a range.

You can make your own offers and choose a range that you’d like to buy

E.g. 0.001 - 0.01