What is the diffrent between bitcoin,altcoin ethereum? Are they same just different name or they they have different role to play in the market wise?
Different coins address different use-cases. I suggest you read the whitepaper of projects you're looking at to get a detailed description of the purpose they hope to serve.
If you're looking for a super quick overview without diving into the details, read -
https://techcrunch.com/2017/11/19/100-cryptocurrencies-described-in-4-words-or-less/