Understand what is happening even you can’t understand every phrase or sentence.
When listening, it is possible to get the ‘whole picture’: information comes in a sequence. And in that sequence of information, there are content words (the nouns, adjectives and verbs) that can help you form that picture.
For example, the words 'food', 'friends', 'fun', 'park' and 'sunny day' have their own meanings, but when you hear the words in sequence, they help form the context of a picnic.