Sounds like what you want is a USB interface with min 2 channels.
Focusrite are one of the go-to options but they cost a lot (£200 for the two-channel option).
This is a more budget friendly option with two XLR-jack combo ports and two channels (so you can plug in via either the jack or the XLR option)
https://www.gak.co.uk/en/presonus-audiobox-usb-96/908317.
If this is something he's really going to get into consider buying a 4 channel thing now and it will give a lot more future flexibility.
Akai used to do their EIE(io) and EIE(io) pro which gave 4 channels but some bad reviews dented sales (usually fuelled by people who don't understand basics on clean-installing drivers and not letting windows tamper with them). I'm not sure if you can still get them anymore. Mine works just fine on win7 and win10 with cubase. Only snag is the badly wired circuit on ALL units (no fix available) which means the intended switch option to monitor 1+2, 3+4 or all 4 channels doesn't work as intended and only allows 1+2, 1+2 or all 4. It's never really bothered me, but might matter to some.
As others have said, Shure SM58 is an excellent dynamic vocal mic (and will also do instruments at a push) and fine for live performing too. It remains one of the default industry mics. Just make sure you buy a genuine one from a legit retailer. There are so many fakes out there.
SM57 is the instrument equivalent. Both are typically £90-120 or thereabouts depending on switched/unswitched
A cheaper option is the AKG D5 which for home use is just as good and offers a slightly sweeter vocal tone. It can be a bit more noisy live, but still not bad, and worth the money for a beginner. Often £50-60ish
For really detailed recording you need condensing mics, with cradle shock-mount and pop shields. A good starter is the Rode NT-1A kit. You'll also want a quiet room as it will pick up everything.
As a general rule condensing mics usually require phantom power. Dynamic mics usually do not.