I want to call Smart Contract function from server side. How can I call? I want to use nodejs.
Any interaction with ethereum smart contracts happens through an ethereum transaction. contract creation is a transaction, contract invocation is a transaction. Transaction are signed with a private key, the signing process happens with the help of a software called "wallet". After the transaction is signed it must be broadcasted to the network. You broadcast a transaction by connecting to any ethereum node json-rpc interface and using the appropriate RPC call.
There is a comprehensive answer about interaction between smart contract and Node-js at here . I suggest read the question in first, after that, see the marked answer there.