What is the significants of Juana and Kinos walking side by side when they return to the town?

Did you mean at the end of the story? KIno no longer feels like a man. He feels defeated. He has lost his child and the Pearl has brought nothing but misery. Juana was right and Kino acknowledges this.

wow Aslan! true true. so due to this realization, Kino is now ready to accept Juana's advice and opinion and to respect her descisions concerning family matters and the direction their lives should take. Hence their walking side by side and not in a single file with Juana behind and Kino ahead as before.