Federations vs confederations

What is the difference between these 2? And what is the best for organising in a socialist or anarchist way?

When googling this there is a lot from a statist perspective, so it becomes useless for our purpose.

Proudhon said:
"In a mutualist confederation, the citizen gives up none of his freedom, as Rousseau requires him to do for the governance of his republic!"

But he also said
"“The federative system is applicable to all nations and eras, since humanity is progressive in all generations and all races, and the politics of federation, which is par excellence the politics of progress”"

CNT is a confederation too

One quote from a statist point of view says:
"By definition the difference between a confederation and a federation is that the membership of the member states in a confederation is voluntary, while the membership in a federation is not."

Does that mean all anarchist organisations are confederations?

But i see many anarchist organisations that label themselves as a federation, like FAI is one: "Federación Anarquista Ibérica"