Schemas? Yes, we said that correctly: S-C-H-E-M-A-S. It's not a dirty word. Even in a key/value store, you will still have a logical database schema of how all the data relates to other data. This can be as simple as using the same key across multiple buckets for different types of data to having fields in your data that are related by name. These querying methods will introduce you to some ways of laying out your data in Riak, along with how to query it back.
A more comprehensive discussion can be found in Key/Value Modeling.