There's a certain mystique around the concept of user personas, but there needn't be.
Developing personas enables enterprises (marketers and designers specifically) to create reliable and realistic representations of specific audience segments. These representations are most useful when they are based on quantitative data (research and analtyics) and balanced out with some qualitative insights and play a major role in everything from corporate branding to interface design (and pretty much everything in between).
The best (most useful and meaningful) personas represent all potential major user groups of a business, focus on the needs and expectations of those groups, offer some insights into who those users are, and provide an opportunity to understand the features and functionality that are most in-demand, describing and highlighting the motivations, goals and values of those audience segments along the way.
There is, of course, no one specific way to create user persona's but there are some details that will time and again prove useful in their development.
Describing the personal characteristics of each persona such as age, gender, and education is a good start but marketers must also understand the professional aspects of each persona. What is the amount of work experience, for example, and why will that persona come to the site or use the service (essentially, what are their goals and professional interests, e.g. career advancement). It's also important to know where else users are getting the information or what other solutions they've used and what has brought them to this point, as well as their technical prowess. Are they power users, for example, familiar with various keyboard shortcuts or are they completely comuter illiterate?
If a persona includes anything however, it should provide a narrative on the motivation of specific audience segments. What are they motivated by and what are they looking for and looking to accomplish? Answer these questions and a clear vision will be developed on how to best attract them, retain them, and generate revenue and deeper engagement with them.
Again, there no one way to create a persona - in many ways, it's a creative pursuit (with very real-world business implications). Take a look at fwe persona's developed for web design solution Weebly to get a better idea of how to construct personas and the information you might want to include as you develop your own.