Do things that connect to internet and transmit data not have to specify what all they send? I get confused with using apps on my phone as well. Most apps seems

Do things that connect to internet and transmit data not have to specify what all they send? I get confused with using apps on my phone as well. Most apps seems to want a lot of information like "Contact list" for a calculator app? I feel the need to learn basic wireless networking enough to know what type of traffic is in a network.