I'm happy to respond, I like talking about this stuff clearly :)

I'll make a few general points that I think will cover most of your questions. Then I'll read back and see if I still need to answer any questions more directly.

In that section, Marx does 3 things at once in order to critique a line from the Gotha program:

1. Takes the line to its logical conclusion to demonstrate its absurdity. (Much like how he critiques political economy in Capital.)
2. Suggests features of a hypothetical transition out of capitalist society.
3. Discusses features necessary for a communist society.

After showing why #1 is absurd, he suggests #2 as a better way to think about it, and finally he brings in #3 to remind everyone what a post-capitalist society would look like.

The Gotha program states: The emancipation of labor demands the promotion of the instruments of labor to the common property of society and the co-operative regulation of the total labor, with a fair distribution of the proceeds of labor."

All the stuff about deductions, that is part of argument #1, showing how impossible it is to build a fair society on the basis of commodities. Who decides what is fair?¹ The law of value is "fair" from the standpoint of the bourgeoisie, because equivalents are exchanged. And in an earlier section, the Gotha program also demands "undiminished proceeds of labor" which is at odds with fairness, because fairness would require deductions (diminished proceeds) for the maintenance of the state, for helping the needy, etc.

After showing in #1 why the program is vague, he acknowledges in #2 that nevertheless, the transitional society immediately emerging from capitalist society would be stamped "economically, morally, and intellectually" with capitalist characteristics. Note morally: people would retain a capitalist morality, like deserving only in proportion to contribution. It will take time to actually transition, from the economic base all the way up to modes of thought, religion, morality, etc. So in the meantime it would likely make sense, even without private property, to organize the distribution of the social product through some sort of labor certificate that works sort of like money, except that it cannot be hoarded nor acquired through exploitation.² This would not be an end in itself, just an intermediate stage.

Labor certificates would still be flawed because they still attempt to distribute products based on fairness, but that fairness is not really fair. Each person may receive equal pay for equal work, but this does not recognize the inequality between persons. For example, one person might have an Olympian physique and be able to work a lot more than someone else who has a physical disability. It reminds me of the quote by Anatole France: "The law, in its majestic equality, forbids the rich as well as the poor to sleep under bridges, to beg in the streets, and to steal bread."

The function of value is to resolve a contradiction, that in capitalism all social labor takes the form of individual private labor. There has to be a determination, for each private labor, how much it counts as social labor. Private labor is not immediately social, it is mediated by a social form, by money/value. In a society without commodities and without value, it becomes possible for labor to be immediately social, for 1 hour of your personal labor to count as 1 hour of social labor, without needing validation by tossing the product of your labor into a market of commodities.

so if something was made in a communist society, its being made to satisfy that need in society and like that use-value?

Yes. Communism would be the production of use-value alone. Or said another way, value disappears at the same time as the commodity.³

At first like people will still have to work like I dunno 40 hour shifts, but over time, that stuff will go down? From like 30 to 20 to whatever?

That's the idea. In capitalism, profit is not proportional to material productivity (of use-value), only value productivity. So the need to labor will never decrease in capitalism, no matter how advanced our technology becomes. It becomes possible to reduce labor in a communist society in which needs are being met, since profit is no longer the driving force.

and to add, that last part, these are some the goals of AES states like China, DPRK, Laos, Vietnam, Cuba, that they're working towards? along with past socialist states. To get to that higher phase of communism. In their own way due to their own material conditions? And to eventually make this part fully realized?

Exactly!