How do I alert process memory use (physical memory threshold)

I would look at the thresholds to see if there is on set to go into warning or critical based on memory and configure those.  Then create your alert based on those thresholds.

I would concur with mharvey's recommendation though this can also be done through the Advanced Alert Manager as pictured below. This example can be easily simplified, but I wanted to demonstrate that you can use both percentage used and absolute (total) values for memory utilization for physical and virtual memory.

I would concur with mharvey's recommendation though this can also be done through the Advanced Alert Manager as pictured below. This example can be easily simplified, but I wanted to demonstrate that you can use both percentage used and absolute (total) values for memory utilization for physical and virtual memory.

Is the value for the alert, memory used, is that in kilobytes/megabytes?

Bytes I'd imagine.

Correct. The value is in bytes. So the example in the screenshot above is 10MB.