起来【qǐlai】

起来 after a verb says the action has started and is now going on. It usually comes with 了, and often with 突然 for something that started without warning.

After an adjective

After an adjective, 起来 says a state is setting in and building: hotter, warmer, busier.

An object goes inside

When the verb has an object, it goes between 起 and 来.

• × 下雨起来了 → 下起雨来了
• × 聊天起来了 → 聊起天来了

起来 or 开始

开始 "begin" names the start as a plain fact and can look ahead. 起来 reports a start that has just happened, often a sudden one, and doesn't go with plans.

• × 我们明天上起课来 → 我们明天开始上课

起来 keeps its literal sense in 站起来 "stand up", and has other uses – 看起来 "looks", 想起来 "remember" – that belong to a separate point.