how to get slow query logs for mysql and analyse it through pt-query-digest?

I have enabled slow query logs in config file. when i execute pt-query-digest filename, it just shows the query-size. It does not show complete output like it is showing for tcpdump option. How to analyse the slow query logs??

Can you show exact commands you used ? I also had written blogpost on analyzing slow log via pt-query-digest worth to read