Hi,
The first sound "am" is the same has "ão" and it sounds just like a dog barking :)), it sounds like "áum".
The second sound "en" sounds like a "nn" a little nasal.
The sound "em" is more open than "en" and sounds a bit like "aínn".
The sound "an" sounds just like it's written "an"
Glad i could help you.