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_v4.ksy --target java
In the case of recordio v4 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, you would just need to run:
RecordioV4 records = RecordioV4.fromFile("/some/record.io");
for(Record r : records.record()) {
...
}