You can use these IDs in functions that have a series parameter. For example, to retrieve the latest value for the CPI Index you can use this function: 

Close(0, ##CPI)

To calculate the 1 year % change which represents the typical inflation number, you can use the function below. Since CPI is updated monthly, and offset of 12 must be used.

%(Close(0, ##CPI), Close(12, ##CPI) )

NOTE: 

For the following indices, we do not receive open prices from our data providers: $DWC, $SPALL, $SPALLENG, $SPALLIND, $SPALLCND, $SPALLCNS, $SPALLFIN, $SPALLINT, $SPALLTCM, $SPALLHEQ, $SPALLPBL, $SPALLGLD, $SPALLEUT, $SP500PG, $SP500PV, $MIDPG, $MIDPV, $SMLPG, $SMLPV, $SPALLPG, $SPALLPV, $SP500EQ, $VIX, $NASDAQ100, $SPALLMAT, $SPALLHEA, $SPALLUTL, $RUId, $RUTd, $RUAd, $RMIC, $TSX, $TSX100, $TSX200, $SPALLREA