In lesson 25, we learn another useful particle 过(guo), which can be used to talk about experiences you have had before. For experiences you have not had, 没有(méiyǒu) or 没(méi) is used for the negation.

For examples,
我爬过长城(Wǒ páguo Chángchéng).
I’ve climbed the Great Wall before.

他没有学过这个汉字(Wǒ méiyǒu xuéguo zhè ge Hànzì).
I’ve not learnt this Chinese character before.