[Q&A] Icon default style

Hi there,

i have recently started modding, so ye, i am a bit of nub in development in android. :(
What i please you to answer me is: How do i set the default icon behavior like when i install a new app, the app-icon will have a default style like it is completely round or completetly square? Also i would like to know how to set it, that the default icon will be stretched into the default frame(square/round). I guess you know what i mean. :)

Thanks in advance for any answer!