I`m trying to understand Bitcoin a bit more, but have a problem I can`t quite figure out, and I`m so unsure about it that I don`t even know how to ask the question (so don`t shout at me!).

How are the "blocks" constructed? on my mining pool I can see blocks being constructed out of transactions, and I know my miner is guessing numbers and when a block is finished the Nodes all get a copy of this new block and the transactions within it, but what part does the fitting of these transactions into a block?

But I`v been told that even if all the electricity on the planet died, all it would take is for someone to spin up a node and Bitcoin`s back in action again (and I assume you`de need at least one miner to start hashing as well).
so if all you need is a node and miner, I`m really missing something in the middle here (I think).
what`s the missing bit? because the info I have doesn`t really make any sense when it`s all put together.

For instance, I consolidated about 30 UTXOs the other day and could see it on Mempool as a consolidation, what part of the Bitcoin machinery is this done on? the Miners, the Nodes or something else I haven`t heard of yet?