[not a bug] where can i see all the cool feature that vim-ledger has?

[JunkyardCat]

currently the ones i know of are
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using the call commands :call ledger#transaction_state_set(line('.'), '*') and :call ledger#transaction_state_toggle(line('.'), ' *?!')

other feature seems to be really vague to me
i am not a master of ledgercli vim or vim-ledger so please help me out

what do you mean by fold transaction?
what does let g:xxxx mean?
what does mean? is it ctrl+x and ctrl+o? i tried doing it but its says pattern not found
where do you use :call ledger#transaction_date_set(line('.'), 'auxiliary')? i tried using this call command it displayed an equal sign and a date. not sure what the purpose of this call is. can you explain