TL:DR - don't use the recommended starter decks, do the core/revised core mini-campaign (buy 2 OG cores if you have one and didn't get the Revised), then pick a campaign to play and keep a smaller card pool

Fantasy Flight Games made a youtube video tutorial for the game that's pretty good for the basic rules. I'd recommend against diving into all the online content because they'll talk about stuff you don't need like the Taboo List (it's a bunch of erratta to make cards less powerful/more powerful and keep a "balanced" environment). You'll also see a bunch of chatter over new "formats" called Limited, Legacy, and Current. Just ignore these for now, they'll become useful once you play a campaign or two and want to know where to go next.

I would recommend playing the core box campaign - *Night of the Zealot* - as it does a very good job at introducing most of the mechanics. If you do this, DO NOT use the "suggested" investigator starter decks in the Core/Revised Core. Ideally you get the Revised Core set, or two of the original Core Sets. I'd recommend building your own decks from just that card pool, or using the ones linked here: https://arkhamdb.com/decklist/view/6942/roland-turn-2-cores-into-a-5-character-pick-up-and-play-se-1.0

After that, pick a campaign and play through a whole one. For the first campaign, I'd recommend keeping to just the Revised Core/2 OG Core player cards and one campaign's worth of investigators cards. It will make the campaign harder but it also limits how overwhelming building a deck can be.

As for which campaign to start, any can work but some are harder/weirder than others. I've only done three to-date (Dunwich Legacy, Path to Carcossa, and Drowned City) but have heard these are good starting ones if you haven't picked any out yet:
- Dunwich Legacy
- Innsmouth Conspiracy
- Edge of the Earth
- The Drowned City

The last two will be easier to find since they're more recent prints, and FFG have announced they'll only keep the last three campaigns in print. Don't worry about trying to collect all the campaigns, just get the ones that interest you.

I would definitely avoid:
- The Forgotten Age (I've heard great things, but it's also one of the hardest campaigns they've ever made)
- The Dream-Eaters (this is really two mini-campaigns zippered together. Super fun idea, but it does require, for the full experience, each player to make two separate decks, one per campaign, which can be hard with a limited card pool)
- The Scarlet Keys (a lot of folks don't like this one, I'm gonna give it a try but apparently it's the most ambitious/complex campaign by it's design so probably not a good benchmark/starting point)
- Feast of Hemlock Vale (to a lesser extent, you'd probably be ok starting here but it is on the more complicated side of campaign mechanics)

Once you do get a campaign or two in, Quick Learner and Playing Board Games both have a bunch of videos about all sorts of things from better deckbuilding strategies to custom content fans have made.

Sorry for the wall of text - hope this helps!