聊 + (着/了/过) + 天
聊天 (liáotiān) is a separable verb meaning "to chat" or "to have a conversation." Because it is separable, other elements like aspect particles can be inserted between 聊 and 天, as in 聊着天 (chatting). It is one of the most common casual expressions in daily Chinese.
我们好久没聊天了,找个时间聚一下。
Wǒmen hǎojiǔ méi liáotiān le, zhǎo gè shíjiān jù yīxià.
We haven't chatted in a long time, let's find a time to get together.
她正在和朋友聊着天,没注意到我来了。
Tā zhèngzài hé péngyou liáozhe tiān, méi zhùyì dào wǒ lái le.
She was chatting with a friend and didn't notice me coming.
我跟他聊了很久的天,聊得很开心。
Wǒ gēn tā liáo le hěn jiǔ de tiān, liáo de hěn kāixīn.
I chatted with him for a long time and had a great time.