How do Wikipedians label articles by their quality level?
What levels are there and what processes do they follow when labeling articles for quality?
In general, Galician Wikipedia articles aren't labeled by quality. There are a few wikiprojects that used labels in past, but they are inactive now.
How do InfoBoxes work? Are they used like on English Wikipedia?
There are a lot of InfoBoxes in Galician Wikipedia, they are at https://gl.wikipedia.org/wiki/Categor%C3%ADa:Caixas_de_informaci%C3%B3n
Are there "citation needed" templates? How do they work?
The principal template citation needed in Galician wikipedia is {{cómpre referencia}}, https://gl.wikipedia.org/wiki/Modelo:C%C3%B3mpre_referencia, but there are others like https://gl.wikipedia.org/wiki/Modelo:Cando, https://gl.wikipedia.org/wiki/Modelo:Clarificar, https://gl.wikipedia.org/wiki/Modelo:C%C3%B3mpre_p%C3%A1xina, https://gl.wikipedia.org/wiki/Modelo:Quen, https://gl.wikipedia.org/wiki/Modelo:Sen_referencias, and https://gl.wikipedia.org/wiki/Modelo:Verificar_credibilidade