The main organisation, in regards to anarchism, in the Spanish Revolution/Civil War was the CNT (Confederación Nacional del Trabajo, or National Confederation of Labour). It didn't spring up overnight, after the attempted coup: it was founded in 1910 (or maybe 1911? I'd need to double check). Anarcho-syndicalism, and anarchism more broadly, had been growing in Spain since the late 19th century. There were a series of other anarchist and anarcho-syndicalist groups before the founding of the CNT, often falling apart due to government repression, but the CNT would prove to be the most successful.

So, in short, there had been decades of movement-building before the Revolution. The revolution wasn't planned, it was brought as a response to the circumstances (there had been smaller, more deliberate uprisings by CNT groups in years prior), but as you seem to be aware, the CNT was quite successful until it was crushed (more by other factions on the Republican side than the Nationalists).

If you're interested, I'd recommend reading: Jose Peirats' 'The CNT in the Spanish Revolution', you can download it free here: https://libcom.org/history/cnt-spanish-revolution-jos%C3%A9-peirats

A book I found to be very interesting in the area is Chris Ealham's 'Anarchism and the City', https://www.akpress.org/anarchism-and-the-city-revolution-and-counter-revolution-in-barcelona-1898-ndash-1937.html which weaves the story of Barcelona as a city (in the more traditional way of thinking) and what I guess you'd call its 'working class history'. This one will also give you a pretty good background of the situation in the decades before the revolution, which seems to be what you're interested in.