Learn cryptography. For free. For everyone.
Edward Snowden, whistleblower and former NSA contractor, wrote in a Q&A at The Guardian that "Encryption works. Properly implemented strong crypto systems are one of the few things that you can rely on." when asked about privacy on the internet.
Privacy is recognized as a human right in the UN Declaration of Human Rights and cryptography helps you with safeguarding your privacy on the internet by protecting your online communication from being eavesdropped, storing your private data such that other can't read them and authentication, which makes it possible to identify yourself to others. But cryptography is difficult to implement correct as Semantics annual threat report for 2015 shows, because most developers don't have the necessary knowledge about cryptography:
of identities exposed via breaches
of emails contained phishing attack
of websites contained critical vulnerabilities
Most likely you used an application today that used cryptography to protect your privacy. E.g. when you update an application on your computer the application have to verify that the received update is from the correct source and not a malicious one. Another example is online shopping and internet banking where a successful eavesdropper could intercept your credit card and private bank informations. To prevent this the communication between you and the shop or bank (the website) have to be encrypted and you have to identify yourself to get access. Finally a lot of people depends on secure communication because they want to protect their company's information from their competitors or they maybe live in a country where having your own opinion could get you killed. In this case, they also need a way to communicate anonymously.
When Julius Caesar sent messages to his generals, he didn't trust his messengers. So he replaced every A in his messages with a D, every B with an E, and so on through the alphabet. Only someone who knew the "shift by 3" rule could decipher his messages.
And so we begin.*