If you're new to PHP or are working to enhance your skills, chances are you've at least heard of the PHP-FIG and the several PSRs that it has released to help provide structure around common functionality. In this article from StarTutorial they walk you through some of the basics of the more widely adopted PSRs including PSR-0/PSR-4 and PSR-3/PSR-4.

Prior to PHP Standards Recommendation (PSR), there were no truly uniformed standards for writing PHP code. For instance, for coding style, some people preferred Zend Framework Coding Standard, and some liked PEAR Coding Standards, and still others chose to create their own naming conventions and coding style.

[...] At the time of this writing, there are six accepted PSRs: two of them are about autoloading, two of them are related to PHP coding style and the remaining are about interfaces. In this chapter, we will discuss each PSR briefly. The purpose of this chapter is to introduce you to the ideas of PSRs. For further details on each one, the respective link are provided.

The post then goes through each of the major PSRs, describing them and providing code examples where relevant:

• PSR-0 & PSR-4 for autoloading
• PSR-1 & PSR-2 for coding standards
• PSR-3 for logging interfaces
• PSR-7 for HTTP message stricture

The post finishes with links to each of the PSRs on the PHP-GIF site for more information.