I am planning on finishing my basement. I am new to this type of work, but have always enjoyed doing it myself.

I will be installing a bathroom in the area that has been roughed in for it. Unfortunately, I am not sure which pipes are which. I have redone a bathroom in an upper floor in another house, but never a basement. There is one pipe coming up from under the slab and another the runs from under the slab to an upper floor, with a capped "Y".
I assume the one pipe is the toilet drain, but I am not sure what the Y'd pipe if for.
Any help would be appreciated.
Thanks.

I have added some pics of what is currently in the basement.
Along with the pipes shown, there is a 3 inch pipe about 17 feet down the wall and 21 feet down the wall. Both pipes are capped.

Thanks again.