Yes, in general they are synonyms but at the same time have a difference, because we use each one in different situations. The verbs "Класть" and "Положить" are the similar, the synonym of this verb can be the verb "Lay", usually we use them when ask or require to do something, for instance:"I told you put it in place!" or "Please, can you put it there". The verb "Поставить" is used the same way, but the difference is in meaning, the best synonym of it will be the verb "Stand", another words the action is the same but we stand the thing vertical, for example:"Could you put this vase on the table". That's all:))))))) I hope you will understand my explanation:)))))))