You will specify the number of shards needed when you create a stream and can change the quantity at any time. For example, you can create a stream with two shards. If you have 5 data consumers using enhanced fan-out, this stream can provide up to 20 MB/sec of total data output (2 shards x 2MB/sec x 5 data consumers).
https://aws.amazon.com/kinesis/data-streams/getting-started/

