It differs from Capitalism in that the associations are free and equal, that workers control the product of their wealth. In mutual aid there is no boss-employee relationship where all the decisions are made by one group and all of the work is done by another. There is no relationship where all of the work is done by one group but all of the benefits go to another. This is radically different from Capitalism. Mutual aid does not necessarily arise out of some feeling of altruism and generosity.
Mutual aid is the logical choice of free autonomous individuals.
In a free society any person who wanted to try to make their own way in the world would be at liberty to do so. However, in a free society no one would enter into a compact with another person in an unequal power relationship. A person going off on their own would be truly on their own, not governing over employees the way 'entrepenuers' do under Capitalism. Mutual' aid is just that, mutual. It's a busy two way street, with no room for parasites.