I am kind of new to this project.I have some doubts regarding Shard,replica
and index.

As per as i know
1.When we create 10k index with 2 shards and 1 replica on node 1 ,then if I
up node 2,node 2 must have 2 shards of 10k memory and node 1 as well..
2.On node 1, 2 shards will be created each shard having 5k memory.
Can u please clarify me whether above two scenarios are correct?

What is the concept behind creating more than one shard on single node or
on multiple nodes?

Its better if u tell about any documents on basics of elastic search terms.