Using the native maps app. Find your current location, by taping on the location icon, in the bottom left of the screen.
This quickly finds where you are, a red pin appears along with a brief address and a blue greater than symbol. Tap the blue greater than symbol. Now you can choose from the centre button share with twitter, email or message (SMS or iMessage)
You can of course share any location, not just your current location. Instead of using the location icon, just search for where you want to go eg "Olympic park" now select the blue greater than symbol.