Logstash, part of the ELK stack, is crucial for aggregating and processing logs to ensure they are parsed and structured for easier analysis and visualization in Elasticsearch. The processing tasks are defined by users in Logstash configuration files, utilizing various filter plugins to transform logs effectively. The Grok filter plugin is the most popular for structuring unstructured logs, while other plugins such as Mutate, Date, JSON, and KV offer specialized functionalities like altering field formats, sorting logs by time, maintaining JSON structures, and parsing key-value pairs, respectively. The choice of plugin depends on the log format, and using a combination, particularly Grok with others, enhances the log formatting process. Logstash also supports additional plugins like geoip and csv, further expanding its capability to handle diverse logging needs.