I have a raster called "aspect" and I want to add 360 to every cells which have a current value lower than 100.
How can I do this using raster calculator?
Using raster calculator assuming you have the spatial analyst extension, you can input the expression:
Con(YourRas, YourRas+360, YourRas, "VALUE<100")
The structure is Con(InputRaster, ValueIfTrue, ValueIfFalse, ConditionalStatement).
See Dan C's reference for more uses of the conditional tool.