In a PPP lesson plan, the teacher presents the new language structure. He or she then introduces a controlled practice activity, meaning that the only language used will be the target language (here it would be complaining). The third P is production or free practice, the students would do an exercise where the target language is very common but not the only language used; e.g. a customer complaining in a shop; a wife complaining her husband doesn't help around the house.
In a skills based lesson plan, the teacher starts out with a reading or listening activity that involves the target language; students are engaged in listening and reading practice. The teacher then asks them to focus on the examples of the target language and uses that for further study and practice.
hope that helps,