Collocations are combinations of two or more words commonly used together, which enhance the naturalness and fluency of English. They can include various types such as verb + noun and adjective + noun, with examples like 'make a decision' and 'strong coffee'. The document also provides several examples of collocations for the verbs 'have', 'save', 'come', 'go', 'get', 'keep', and 'catch'.