The generations start with USB 3.0.

But for bonus confusion they don't refer to connection speed. They refer to single lane speed, and a connection can have 1 or 2 lanes.

Gen 1 is 5Gbps, gen 2 is 10Gbps. Gen 2x2, sigh, is 20Gbps total. If they weren't trying to obfuscate things, those would simply be 3.0, 3.1 and 3.2.

There's also Gen 1x2 in theory, but I've never seen mention of anything using it.

And then after USB 3.2 you have USB4[sic] which adds Gen 3 and 3x2.