How do I use popular music in YouTube videos?

Pay licensing fees.

Agreed.

Musicians are intellectual property holders (or they have sold or transferred the rights to someone else) and using their music requires paying licensing fees.

Don't want to pay licensing fees? Then you have three choices:

1. Don't pay and get your videos taken down by YouTube. If that happens enough times, YouTube will suspend your account. Plus the IP holder might issue DMCA takedown notices and even sue you. Way more expensive than some licensing fees.
   
2. Use public domain music. YouTube offers lots and lots of it. You can get other less expensive music on sites like Fiverr but be aware that those might still be licensed works and the seller could be lying to you about ownership or public domain status. At least YouTube won't lie to you about whether a tune is in the public domain.
   
3. Don't use music at all.

Not to overly complicate matters, but there is such a thing as the fair use defense and you could conceivably try it if you were sued. However, among other things, you would be better off if your videos were not commercialized (e. g. monetized, where YouTube shows ads and you can get a cut of the profits) and they were educational. The law is a bit in flux when it comes to fair use but commercial use tends to fail the fair use test whereas educational use is a lot more likely to pass it. But neither are guaranteed, and intellectual property attorneys are expensive whether you win or lose.