What is the difference between Bitcoin and Ethereum,& advantage of etherium.

Well, Bitcoin was inherently designed to act as a medium for value storage and transfer while Ethereum provides a platform (and even its proper programming language) for developing applications that are only limited by the imagination of the developers. So it is possible to issue a new cryptocurrency on top of the Ethereum Blockchain protocol. In a nutshell, Bitcoin is just a single application of the Blockchain technology whereas Ethereum is a flexible programming platform built on top of a Blockchain.
Similarities between Bitcoin and Ethereum include using the Blockchain technology (obviously), both tokens can be mined, the use of proof of work to validate generated blocks and many more.

#advantages -

Decentralization: like Bitcoin, the Ethereum Blockchain is distributed across all nodes inside the network, so is power and influence, which means no central authority can censor, destroy, or interfere with Ethereum. No need for third parties. This also means that even if a part of the network fails for some reason, the Blockchain and all applications running on it will survive.
Cost effectiveness: low costs and fees due to the removal of middlemen.
Immutability: as long as the network is run by a majority of “honest” nodes, nobody can alter anything on the Blockchain.
Security: all transactions in the Ethereum environment are cryptographically-secured.
Smart contracts: applications on the Blockchain that can self-execute according to the code governing them and manage all necessary operations automatically, eliminating trust barriers and third parties.