How to test MongoDb sharded cluster
The tutorial refers on how to setup a sharded cluster but not on how to shard collections. 

The next step is to enable sharding for a database and shard one or more collections in order to distribute the data.

From the mongos first use sh.enableSharding("dbname") https://docs.mongodb.org/v2.6/reference/method/sh.enableSharding/

and then sh.shardCollection("dbname.collectionname",{shardkey:1}) https://docs.mongodb.org/v2.6/reference/method/sh.shardCollection/

You need to choose what the shard key will be. A tutorial on how to choose a shard key can be found here  https://docs.mongodb.org/v2.6/tutorial/choose-a-shard-key/