how can you translate english words ending in -ing into spanish'
Words ending in -ing can be gerunds, past participles, or words that happen to end in -ing, like Earthling.
sing/thing/bring et al. would have been better than Earthling (sing "-ling" is a legitimate diminutive suffix).
Words ending in -ing can be gerunds, past participles, or words that happen to end in -ing, like Earthling. Each of of these kinds of words will be translated in a different way depending on the word itself and what you want to say, so in order to answer your question, we'd have to write a whole book to cover every single possible translation. English and Spanish and different languages, and you won't be able to find a one-to-to correspondence between words all the time; sometimes verbs in -ing will translate as verbs in -ndo; sometimes as infinitives, sometimes something completely different. Can you please narrow down your question?
In any case, this is a very typical question, and it has been answered before, so please do a search first.