Lets take a step back to explain what's going on. Back to the 90s.
Doing business in Europe was a pain. An Italian buying a French vehicle had to convert lire to francs, and the French had to convert francs to Deutsche Marks when importing from Germany. Everyone involved took risk that someone else currency would fluctuate, leaving them with a loss.
To simplify things for everyone, europe adopted the euro currency on Jan 1, 1999. It became simpler to do business with neighbor countries increasing trade in theory.
This setup is siilar to the US where 50 individual states share a single currency. The difference is the 50 stats have a central government that collects taxes, runs the military and so forth. It's important as no matter what state you live, the government has your back. The rich stats subsidize poor states, creating cohesion and semblance or order under a single currency.
Europe doesn't have a central government. Each country collect it's own taxes, creates it's own social insurance, funds it's own healthcare, all with great differences. Because low-debt countries prosper with a strong currency, while unproductive high-debt countries actually need a currency that loses value, there is a problem. Knowing this could be a problem, the euro pact set guidelines banning big deficits. Greece didn't follow the rules, running up huge deficits.
In 2010, the world wised up there started the Greece shit. Normally, this would cause a deep recession as Greece's currency will plunge, but ultimately put it's economy back on track but Greece didn't have it's own currency. It has Euro. Which meant it couldn't inflate debt away with cheap currency.
Budget cut's to Greece sent it's economy into utter shit hole. Unemployment hit 28% in 2013, worse than the U,S during the great depression. A new government, the Syriza party promised to stand up against the foreign creditors and here today after calling each other's bluff, Greece said there would be no more budget cuts and lenders said there would be no more bailouts. Greece lost the showdown last week and this sets Greece up to default on it's debt.
What a mess, personally I feel it's best Greece just gets the fuck out of the Euro. Greece it's like your gambling family member. Or that pest you can't get rid off. Eventually one day, people will get enough of crap.