Jakub ->You should use Fopnu to share files with your Dad.
-both of you download and run fopnu.
-one of you makes a channel. the channel can be private or public. (this page will help: https://support.fopnu.com/GUI/Chat
-whoever made the channel, right click the channel in the chat window and select 'copy link'. now send that link to the other person through email or however you want.
-now they add the channel to their fopnu and start the channel.
or you can both enter the same channel and if you know each others name contact each other that way.
be sure to add each other to your contacts list. it will be easier to find each other in the future.
this page will help with sharing files publicly and privately: https://support.fopnu.com/GUI/Library