Do the events (whatever actions done by users) from Dapp are considered as Transactions? If so, is there any need for the users of Dapp to hold EOS tokens? How these transactions are reached to Block producer?
Any event (action) that occurs on an eosio chain is at least a part of a transaction. The transactions are sent to a node that either belongs directly to a block producer, or will be forwarded to one. When sending transactions, resources are used up and can not be reused for 24 hours. These are CPU and NET bandwidth, and possibly RAM. In order to access these resources, they either have to be delegated or bought.