Pgtune works by taking an existing postgresql.conf file as an input, making changes to it based on the amount of ram in your server and suggested workload, and output a new file.

pgtune will add a set of configuration values at the end of the output file.

pgtune will set values for variables like maintenance_work_mem, effective_cache_size, work_mem, wal_buffers, checkpoint_segments, shared_buffers or max_connections