过【guo】

过 straight after a verb says the thing has happened at least once before now. It is about experience, not about when.

The sentence claims only that the experience is on the record. When it happened, and whether it will happen again, are not part of it.

过 or 了

了 reports a particular completed event. 过 reports that the event has occurred at some point.

A broad time like 以前 or 小时候 sits fine with 过. A time that pins down one occasion, like 昨天晚上, usually means 了 is the marker you want.

The negative keeps 过

没 removes 了, but it leaves 过 in place. 过 stays straight after the verb, before the object.

• × 我没去中国过 → 我没去过中国

从来没…过, as in the second example, makes "never" emphatic.

How many times

The number of times, with 次, follows 过. A noun object usually comes after it; a pronoun comes before it.

A question takes 吗 or 没有 at the end, and the answer is 去过 or 没去过.