We often use ONE instead of repeating a countable noun.
"Which dress would you like?" "A very elegant one!"
"It was a good meeting, why don't we organise another one next month?"
The plural is ONES.
"I like all sweets but I really like the chocolate ones."
"Which books do you want?" "I think I'll take the cheapest ones!"
We never use ONE for an uncountable noun.
"Would you like some coffee?" "Yes, black (coffee), please."
If there is no adjective: we say ONE, not A ONE.
"Is there a swimming pool near here?" "Yes, there is one near Bridge Street."
We use SOME and ANY without ONES. We use mine, etc instead of my one, etc.
"Can I borrow your tennis shoes for the weekend?" "I'm sorry but I haven't got any."
"Which computer can we use?" "Let's use mine!"