I'm supposed to be learning Infinity , but I dont know what book to get.

Is N3 the current rulebook? My local store has it but thinks its old.

N3 is the current rulebook. All the rules are actually available online. The lore is exclusive to the print books only.

https://www.infinitythegame.com/resources/downloads

It can overwhelming for beginners. Your best bet is to go through the quick start rules, or have someone take you through the two player missions. The majority of the rules are special skills and equipment, so once you learn the basics, you can just focus on the skills that your army uses.

Pick up Operation Red Veil, Ice Storm, or Cold Front. Great minis for two players, scenery, dice, bits, and rules to ease you in over 5 games that progressively add more content. About <$80 online for any of the three that fits your taste. You can expand with their “Beyond” boxes.

Tons of great content on YouTube, won’t take you long to find it.

The Corvus Belli website/forum is super active and lots of friendly people there to converse with.

Great game. I’m basically only playing Infinity and Legion these days, have sold almost everything else to fund these two.