Some important cards I can think of off the top of my head: The Power 9, the boon cycle (lightning bolt, dark ritual, giant growth, ancestral recall, and healing salve), Shivan Dragon, Birds of Paradise, Llanowar Elves, counterspell, wheel of fortune, and Wrath of God are all extremely iconic cards from the first sets and are referenced by the community and by other cards a lot. There are many other older cards like force of will, Necropotence, Juzam Djinn, and mana drain that are also very iconic.

Some newer cards that are very famous include the original planeswalkers from Lorwyn block, Slivers, Eldrazi, Phyrexians (especially the praetors), the Theros Gods, and characters like Urza, Nicol Bolas, Yawgmoth, Mishra, Teferi, and Karn are all very important in the magic stories, and many have multiple cards.

Colossal Dreadmaw, Storm Crow, and Questing Beast are the biggest meme cards, so you should probably be aware of those.

Someone's working on the cardfetcher bot, but it's not ready yet.

If you're looking for cards you can play in your kitchen table games, you could include of these iconic spells that help counter your opponents strategies. Just be aware that delving too deep into strong, flexible cards like these could kick off an arms race!

White: Oblivion Ring, Wrath of God

Blue: Unsummon, Counterspell

Black: Murder, Distress

Red: Lightning bolt, Abrade

Green: Prey upon, naturalize

Power 9 are classics. They're some of the most powerful cards ever printed.

It depends on the format. Each format will have a list of staple cards that you will see over and over again in lists, but it varies based on what type of game you will be playing

I would definitely say familiarize/love/hate good ol Sol Ring