Hi and welcome,
The introduction course of mendix (online course here: https://gettingstarted.mendixcloud.com/index3.html ) shows you how to use values entered by a user (short answer: forms)
Enumeration values is like a fixed set of options to be used by microflows, user etc.
I recommend you follow the training, it will give you a basic understanding of how everything works and should answer 1 & 2.
3. can be done by creating a microflow that calculates the fare value.