Once you have your wallet set up, you can buy bitcoins online (in some cases directly through the wallet provider) or offline, you can earn them, or you can create them by becoming a miner.
Online bitcoin exchanges will sell you bitcoins for any of a wide range of fiat currencies (dollars, euros, yuan, yen, etc.). Kraken, Bitfinex and Bitstamp are just some of the main ones, and several offer wallet services in which to store the bitcoins you buy.
In many cities, you can buy bitcoins physically. LocalBitcoins, for instance, will post bitcoin offers, and it’s up to you to arrange to physically meet the seller to exchange cash for a bitcoin transfer. Some cities have regular gathering spots where you can just show up and offer cash in exchange for digital currency. You hand your cash to the seller, and he or she transfers bitcoin to your electronic wallet with a few taps on his or her computer or phone. More and more cities have bitcoin ATMs, where you feed your cash into the machine and then hold your bitcoin address (in QR code form) in front of the scanner so that it knows where to transfer the equivalent amount of bitcoins to.
You can also earn bitcoins, just as you can earn any other type of currency, by working for them. Several companies prefer to pay their employees in bitcoins, especially if that’s the currency that the business operates in. And the subreddit Jobs4Bitcoin posts one-off tasks that will be paid in bitcoins.
The most complicated way of earning bitcoins is by becoming a miner. You’ll need a very powerful processor (the current standard is ASICS) onto which you download the Bitcoin program. You then compete against other miners to solve a mathematical puzzle that at the same time validates a block of transactions and adds it onto the blockchain. If you get the right answer first (which depends mainly on guesses and very fast computing), you earn 25 bitcoins (this amount halves every 4 years, in approximately 2017 it will go down to 12.5).
These methods of acquisition may remind you of another currency from hundreds of years ago: gold. Back then you could get gold by mining it, by earning it or by buying it. Like gold, bitcoins are backed by no-one. Like gold, bitcoins are not in unlimited supply. I think that we can all agree that bitcoins are easier to carry.
(For more on how Bitcoin works, see Bitcoin Basics.)