I'm not mechanically inclined, but thanks to COVID and Youtube and a shortage of bike mech services in the area I've taught myself to replace most of the groupset on two bikes. However, I need a bit of help understanding how to examine a rear hub and modifying a cassette to go from 10 speed (Shimano, Ultegra preferably) to 11 speed.

Here are the facts:
- I'm working on a 2005 Litespeed Ultimate,.
- I would like to replace the 10 speed cassette with an 11 speed. The shifters and the derailleurs have been done, mostly by waiting for good deals on eBay. That is why things were not done in the proper sequence.
- How do I know if the rear wheel (which dates around 2010 since it came with another bike) has a hub that is compatible with 11 speed?
- Does hub compatibility have anything to do with wheel axles?
- I understand that if the 11 speed cassette is compatible with the wheel's existing hub, then the difference 10 speed and 11 speed is spacing between the cogs. An 11 speed cassette is 1.85mm 'thicker' than a 10 speed cassette. Does that mean that all I need to do is buy another cog (for a total of 11) and swap the spacer closest to the hub? Is it the spacing between all the cogs that is different? How does it line up with cable pull in the shifter and the derailleur?

I do Google all of this. The problem isn't so much that I don't understand the instructions, it's that I have a hard time with the terminology since there's no one around to point out the parts. If anyone can provide a Dummies 101 explanation of a hub and spacing I would be most grateful. I don't want to order an 11 speed cassette and then realize that in fact I needed an entire new wheel first.