Shimrod is perfectly correct. On all points, really... ;-)

Nettles are very tasty, an excellent source of iron, and fabulous for the compost bin (provided they're not loaded with seed!). The time of year doesn't matter. As with many vegetables it's about the size / coarseness. If you cut them later in the year, take the nettle tops, the young leaves. The flavour, I usually describe as "tannic spinach". They certainly don't sting once cooked. If you really want to try them as a salad... :o ;-)