It's an expansion, the seventh, for characters in the level 110-120 range. So it will take time to reach shadowlands, unlesss you buy one of the collector versions which allow you to create a level 110 character. Or you could create a demon hunter which start at 100.
Wow classic is more or less the original came without expansions, shadowlands is not part of classic. But if you buy wow and subscribe, you get both classic an the current game.
Some here will say that mmos are a waste of time. Others will say that wow was much better 15 years ago. I say that if you like mmos it's worth trying. I'm having fun. Mindless fun, but still fun. If you don't like mmos, stay away from it.
WOW requires a paid subscription. Otoh, microtransactions play only a small role in the game compared to socalled free to play mmos.
A pibbur who will look for typos when he comes home.