A recent post on the EPLAN forum reminded me that I once had a difficult time understanding the meaning of the icons in the EPLAN navigators. There is a good online resource describing these in the EPLAN help file and there is also a nice laminated card included with the second edition of the Bernd Gischel P8 reference handbook. However, both of these resources assume that you fully understand the meaning of certain key words such as function, auxiliary function and other important terms.
When I started to teach EPLAN classes I realized pretty quickly that I needed to describe this topic in a way that new users would understand, so I created several power point slides for my training class which I have included here as a downloadable PDF.
I hope that it helps you to better understand this important topic, if you would like for me to add anything just send me an email.