Step 1: Find a picture
There are a number of sources out there. Tumblr is a huge resource, as well as WeHeartIt. However, sometimes these images are under copyright and their owners might come yelling at us. Flickr has a huge, searchable collection of public domain images you can play with, as well as a ton of Creative Commons-licensed photos. (“Hipstamatic" is a good keyword to search for!) Be sure to credit your source with a click-through link.
You can use your own photos too, of course. The Rowsdower that started this blog was my own awful photography. ;)
Step 2: Find a way to add text to your picture
If you own Photoshop or a similar program, adding text to an image should be easy. If those programs are too expensive, you can download free equivalents like GIMP. But there are also several online services out there (like PicFont or Image Edit) that allow you to add simple text to an image.
Step 3: Choose a font
Arial or Helvetica with no outlines or shadows look best. Hipsters love minimalism.
Step 4: Choose your quote, add the text and submit it!
PRO TIPS: If you have Photohop or GIMP or the like, you have more tools to use. Try reducing the opacity of the text. Change the blending mode from Normal to Screen or Multiply. Create a work path from the text (via right-click) and then add an adjustment layer (like Invert). Experiment and have fun!