The thing that you want to measure should go in “Value”. Your categorization, i.e. the slices of your pie chart, should go in “Group/Color”.
If you don’t already have a field that represents the slices of your pie chart, you have to create one. Something like this:
Category = ifelse(
{days} > 365, ‘365+ Days’,
{days} > 270, ‘271 to 365 Days’,
{days} > 180, ‘181 to 270 Days’,
{days} > 90, ‘91 to 180 Days’,
‘0 to 90 Days’
)
Then put Category in “Group/Color” and put whatever you want to measure in “Value”.