This is extremely reductionist as it’s actually a fairly complex school of thought, but it’s essentially just: everyone is equal and thus should have equal rights and treatment under the law. A basic example:
I have a cake and take it to a party with 7 others. We agree everyone should have equal right and access to the cake and so cut it into 8 equal slices.
Where as Capitalism is like: I decide because I came up with the idea of getting cake, I deserve more of it, so I take 50%. The host of the party gets a 20% cut. And the remaining 6 guests divvy the remaining 30% amongst themselves.
Ah yes, @bikini.bottom.news!