Resolution:
This is to insert the globalvariable in a field. Although you can type in the field the global variable name, using "insert" can avoid typo and ensure the global variable is defined.

For example, a Generic Adapter Configuration-&gtAdvanced-&gtSession-&gtRVSession has a field named "Service." If you want to replace the default %%RvService%% with your own global variable, say, "myService", delete the %%RvService%% and place the cursor in the field "Service". Goto Edit-&gtGlobal Variables, select "myService", and now you will see the "Insert" button enabled. Click the "Insert" button and you will see %%myService%% is inserted in the field RVSession-&gtService.