1. are bralettes meant to be seen? or is that only bandeaus? 2. can i wear a low cut arm holes tank top with only a bralette underneath?

1) Bralettes are usually worn underneath sheer clothing/muscle tanks/etc. And you can also wear it on its own. 2) Yep!

bralettes are like bandeaus except they can also be worn by itself with high waisted skirts or shorts

Barlettes are okay to be seen. And yes, you can wear it with that shirt. :)