elasticsearch.yml and kibana.yml don't need any special configuration for processing txt files. This is all handled by the logstash config file. I would start with something like the example here: https://www.elastic.co/guide/en/logstash/current/config-examples.html#_processing_apache_logs
Obviously this isn;t exactly what you need but it has a file input and an elasticsearch output. If you change the path parameter to match the file pattern for your txt files and remove the filters you should have something to start with. Then (if you need to) you can add filters later to extract information into structured fields. The exact configuration you will need depends entirely on the structure inside you txt files.
If you need to ask specific questions on logstash or you are having issues indexing into elasticsearch using Logstash you can ask questions on the Logstash Category. Please remember to fully describe your problem, include any errors and your Logstash config file (paste this into a gist and link to it if your config flle is long) and also describe what you have tried so far.