The best about Kaitai is its excellent documentation. You can find how to install and use it from their website. Below we make a quick example on how to compile and use it in Java, other languages work the same way.
All we need here is the ksc command (or kaitai-struct-compiler), the respective ksy file and the target of compilation.
Here, for example, we compile for Java:
ksc recordio_v2.ksy --target java
In the case of recordio v2 we need receive two files: one for the vint compression schema and one for the actual recordio files.
The Java code is fairly easy to use (even though it doesn't that intuitive), you would just need to run:
RecordioV2 records = RecordioV2.fromFile("/some/record.io");
for(Record r : records.record()) {
...
}