Let's say you want to get a count of the Computer block in two areas.
Specify the first area on the Count Palette
Then right mouse click on the Computer item and select Insert Field
Then double click on the inserted Field and copy the expression shown onto Notepad

Repeat with the second area.
Then enter FIELD command > Objects > Formula > right mouse click within the Formula window and select from the cursor menu Insert Field

On this FIELD window > Objects > Select CountInArea paste into the Expression window the contents from the copied expression from area #1 and click Evaluate to see the count in the Preview then click OK.

Back in the original FIELD window enter the + symbol and right mouse click and select Insert Field again:

On this FIELD window > Objects > Select CountInArea paste into the Expression window the contents from the copied expression from area #2 and click Evaluate to see the count in the Preview then click OK.

Click OK to insert the count total as a FIELD into your drawing.