@Soi Ooof there's both a lot to know and it's hard to know what to say.
Even though it risks becomes a bit of a box ticking exercise the Nook Miles + app on your little phone thing (the top centre icon when you press ZL) is a good guide. You earn Nook Miles for speaking to villagers, finding and getting fossils assessed, catching certain fish, whacking rocks etc. so it becomes a good daily checklist on what to do. Those Nook Miles can be exchanged for items in the Nook Terminal in Resident Services.
If it is early on Nook in the Resident Services gives you little tasks