Did you know that you share 50% DNA with your biological parents and siblings (each)
You share 25% DNA with your biological grandparents, nieces/nephews/etc. and aunts/uncles/etc.
You share 12.5% DNA with your first cousins
You share ~3.2% DNA with your second cousins
You share ~0.7% DNA with your third cousins
And you share ~0.2% DNA with your fourth cousins
If you have an identical twin, are in identical triplets, quadruplets, etc., then you share 100% DNA with them!
The rank of cousins depends on how they are related to you by your family tree's generation before your parents (grandparents, great-grandparents, so on)
First cousins - Same grandparents
2nd cousins - Same great-grandparents
3rd cousins - Same great-great-grandparents
4th cousins - Same great-great-great grandparents
And so on...
And the "____ removed" is if they're one generation different than you in technical terms (Boomer, Gen X, Millenials, Gen Z, Gen Alpha, etc.). Only for cousins for some reason.
Cousins once removed - one generation difference than you
Cousins twice removed - two-generation difference from you
Cousins thrice removed - three generations difference from you
ETC.