ExBinance.Private.create_order

You're seeing just the function create_order, go back to ExBinance.Private module for more information.
Link to this function

create_order(params, credentials)

See ExBinance.Rest.CreateOrder.create_order/2.

Link to this function

create_order(symbol, side, type, quantity, price, time_in_force, credentials)

See ExBinance.Rest.CreateOrder.create_order/7.