How to build a class diagram and a state diagram for the "mobile bank" system?

Question

Software design

Good afternoon,
tell me, please, what objects can be selected when compiling the state diagram of the "mobile bank" system?
Can I choose "payment for cellular services" and "transfer of money from account to account", for example? And then just describe further states (for example, when transferring from account to account:
-selection of the operation "transfer to another account",
-selection of the account from which I want to transfer money
-selection of the account to which I want to transfer money
-selection of the transfer amount
- balance check
- operation execution)?
It turns out a sequential unbranched diagram. Or am I mistaken and these are not states, but actions? Then what states can be?
And one more question: in the activity diagram, actions in one state or another are simply described in detail? That is, the process is the same, but with conditions, choices, etc.? (for example, when checking the balance, the system can give two ways: the money was transferred, because the amount is less than the amount on the account and the request was rejected, because the amount is greater than the balance on the account)? Thanks in advance. Sorry if this is a dumb question, I just started learning and I don't understand much. I read literature, shovel the Internet, but, since the study is remote, there is no one to ask questions.

Answer 1

"Horses mixed up in a bunch, people." An attempt to describe the system in general from all sides will not bring any benefit, and it is not possible to do this in general clearly and clearly. It is worth starting at least with use-case diagrams to understand what actors are, and from there it will be possible to make a component diagram and go further. The conditions for riveting are not about design, but if everything that I have listed is difficult for you, then just take a mindmap