The nut broke off and had a small red ring/gasket between these connectors. I’m an noob but can follow instructions. Please give suggestions. Thanks
Below there is a water valve 
which may be used as an alternative if the above (cupper?) pipe is inconvenient to use.
I think moving farther down to a straight area and cutting there to add a compression fitting or union would work better.
Since either one would add length, it gives OP something to work with.
Buy a new fitting just like what’s on there (only for the nut), and a compression coupler.
Cut the pipe say 6" above the valve, slide on the new nut. Attach nut finger tight.
Put compression coupler (without rings or nuts) on standing pipe, check needed length in pipe to fitting, cut as needed.
Now disconnect it all, setup compression fitting with rings and nuts ok both sides. Again finger tighten the new nut. Double check it all fits well, then tighten everything down.
This way you don’t have to solder anything, let alone deal with that bend and fitting.