sec/tert vs neo/iso

[Claire Polizu 3B]

I still don't understand when to use sec/tert vs neo/iso-- could someone clarify it?
Is the latter just used when giving the common name?

[Chem_Mod]

When naming substituents, sec tert neo and iso can all be used as part of an IUPAC name (it is ok to use isopropyl instead of methylethyl, for example). The IUPAC name with substituents that have common names is still an IUPAC name

However, when naming compounds (only iso and neo applicable here, sec and tert can only describe substituents), if you use iso or neo to describe the compound as a whole, it is no longer an IUPAC name (eg. neopentane is the common name for 2,2-dimethylpropane)

[Stephanie_Younan_3D]

How can you tell the differene between sec/tert and neo/iso when looking at a picture of a structure?