Yajuj Majuj are two tribes which are mentioned in the quran after dajaal will get killed these two tribes will come out from where they are hidden and they kill and eat anything that gets in there way,they are human but will be deformed and structured differently,Zul Qarnain is a king who is mentioned in the quran ,people complained to him about yajuj majuj that they are causing problems within the community,so then Zul qarnain built a huge wall,to keep them away from the rest of the people.
Yajuj Majuj will not be released until dajaal is killed,when they are released they will come out in full force,they will be die,when Prophet Isa alayhisalam will make dua to Allah Azzawajjal,when they are wiped out,Allah Azzawajjal will send creatures similar to birds,that will come and pick yajuj majuj’s bodies up from the world and the birds will throw their bodies away.
Until, when he reached [a pass] between two mountains, he found beside them a people who could hardly understand [his] speech. They said, “O Dhul-Qarnayn, indeed Gog and Magog are [great] corrupters in the land. So may we assign for you an expenditure that you might make between us and them a barrier.
There are many more signs of judgement day,but Yajuj and majuj is one of the major signs of judgement day… Yajuj and majuj will come after dajaal will be killed by Isa alayhisalam,however when yajuj majuj come,they will not be able to be killed,only by doing dua ,will put them to an end.