Let's go through the words. "Corrio" comes from the verb "correr," which means "to run." The suffix "-io" is the past tense of the el/ella/Ud. form. So, "corrio" means he/she/you/it ran.
"Cerca de" means close to, so that's probably a phrase. "Bicicleta" is bicycle, and that's a female noun, so we'll have to put the "la" (female "the") in front of "bicicleta."
"Perro" is a dog. It's a male noun, and "un" means "a" for a male noun, so these probably go together to. "Muy" means very--this probably also goes with "close to," describing a position.
So translated, we get: "ran the to close bicycle dog very a." Let's review the phrases we have: "a dog," "very close to," and "the bicycle." All that's missing is "ran," which must go after the dog. So, "a dog ran very close to the bicycle." That's a reasonable sentence!
Let's translate it back to Spanish. "A dog" translates to "un perro," "ran" to "corrio," "very close to" is "muy cerca de," and "the bicycle" is "la bicicleta. What do we get? "Un perro corrio muy cerca de la bicicleta."
