The number_of_shards defines the number of primary shards and the number_of_replicas is a replication factor of the primary shards.
The formula to define the total count of shards of number_of_shards * (1 + number_of_replicas)
So, in your example, if you define 1 shard and 0 replicas, then you will have 1 shard only for this index, and not 3, regardless of how many nodes your cluster have.
If you define 3 shards and 2 replicas, then this index will have 9 shards in which 3 are primaries and the other 6 are replicas.
There is a diagram here https://www.elastic.co/guide/en/elasticsearch/guide/current/replica-shards.html that explains this better.