"leyendo" and "lectura" both mean "reading". How does one determine which to use in a sentence?
Are these words context sensitive?
"Leyendo" means "Reading" - the verb. "Estoy leyendo la novela" - I'm reading the novel. "¿Qué has estado leyendo?" - "What have you been reading?"
"Lectura" is reading, the noun: "Me gusta la lectura" - "I enjoy reading"
"La lectura es importante para los niños." - "Reading is important for children".
Lectura is a noun and it means "reading." I like to do a bit of light reading before bed.
Leyendo is the progressive form of the verb "leer." I am reading a book right now.
Note that verbs ending in -ndo are in the present progressive tense, which means that it is being done right now.
I think that Gekkosan and Marianne gave great explanations already, so I will leave it at that.