Answer:
Basically it creates a unique identifier for each row in your table and that can help you link your table to other tables using primary key as link
Explanation:
"Primary key allows you to create a unique identifier for each row in your table. It is important because it helps you link your table to other tables (relationships) using primary key as links."
Nope those are quite rare but are found at qdoc.tips
Using group video conferencing , for example skype would be a great way to do this efficently with good audio and video and all would be able to communicate and send files together