What episodes are important to the lore?

Like, the main plot through the series. For example, the first seasons talk about Eric's dad and they solve this finally on the 14th, I think, in the 201. There's the Mrs. Garrison part too, with the surgeries, ups and downs, homosexuality... I mean, they develop some stuff in episodes throughout the series.

I watch episodes randomly, and I see that in the recent eps, cartman lives in a hot dog old food truck, Stan lives in a weed farm, there's lookouts of new characters and all, I get kinda lots.

Is there any kind of guide?