Hello Syed Ezaz Ahmad!

Sorry, but your question is too wide. You may refer to the next manuals for the beginning:

1) customize via Stuido->Designer app https://github.com/unaio/una/wiki/Designer

2) create own template app https://github.com/unaio/una-vendor-template

You may read other sections from our Wiki too https://github.com/unaio/una/wiki