>抱怨 : you are tired of sth, or don't like something and u can not stand it any longer, so u wanna express your feelings out, then you 抱怨 those stuff. similar with complain or grumble.
1. 工人抱怨说没有获得工资. The workers complained that they did not get the pay.
2. 请不要抱怨了. Please stop complaining.
>诉苦 : u r suffering from sth a lot, and you wanna tell this to sb else.(sb else only)
1. 他对我诉苦道:他过去受了很多苦. He told me that he suffered a lot before.