To export/share your deck, go to the Export/Share section of the deck's details page.
You can share your deck with friends using the sharelink at the top of the page. Copy the link and send it to a friend and they'll be able to browse and playtest your deck! Make sure to make your deck public by checking the box marked Public, on the deck's details page.
You can generate a decklist registration by clicking the "Create PDF" button in the middle of the page. This will open a window where you can fill in your details and those of the event. The decklist and personal/event details will be added to a form which you can download by clicking the "Create PDF" button.
Finally, you can export your decklist as a .CSV file. This is useful for keeping an offline backup of your deck or to import it into another program (eg. MTGO or MTGA).