"¿Tú caminaste por la playa ayer?"
Translation:Did you walk along the beach yesterday?
"Tú" is a null subject. A "null subject" does not have to appear in the sentence or be said allowed. It is understood.
How are you suppose to know the difference between"along" and "on"? I thought "por" could mean either?
"Did you walk at the beach yesterday. " What is wrong with this? Where does the along come from?