How read a bottle label and buy and try grapes, luscious sweet wine, Sauternes style

What does this mean? Grains nobles, in French, translates into Noble Rot in English.

In a late summer, in England called an Indian summer.
You can get the grey mould earlier in the year. But later - the
amount of sugar is same but the grape skin splits and water evaporates leaving a concentrated flavour.

The capital letter of Sauternes should give you a clue that it is a region. Wikipedia says:

Sauternes is a French sweet wine from the Sauternais region of the Graves section in Bordeaux. Sauternes is made fromSémillon, Sauvignon blanc, and Muscadelle grapes that have been affected by Botrytis cinerea, also known as noble rot. 

If you are not into wine, here are some grapes bought in London from La Fromagerie (near Baker Street station).