聊天儿 (liáo tiān r) is a colloquial, separable verb meaning 'to chat, have a chat' — it specifically refers to casual conversation, unlike the broader 说话 (shuō huà 'to speak/talk'). It is the full, erhua version of 聊 (liáo), used especially in Northern Mandarin; the object 天儿 is often separated (e.g. 聊了一会儿天儿).