Normally, CAD users can either click on a command icon and then select an object or select an object first and then click on the command icon, both will do.
But what to do when you can’t select objects before running the command?
If you find selecting objects before a command is no longer working, set the PICKFIRST system variable value to 1.
The PICKFIRST system variable controls whether users need to select objects before starting the command.
The initial value is 1, which means users are allowed to select objects before starting the command.
If the value is set to 0, users can only select objects after starting the command.
Other system variables concerning object selection: PICKAUTO and PICKADD
PICKAUTO controls automatic windowing for object selection, if the value is set to 0, the CAD system closes automatic windowing selection and crossing selection; if the value is set to 1, which is also the initial value, the CAD system starts window or cross selection when clicking if the cursor is not located on objects.
If you cannot select multiple objects, check your PICKADD system variable as in the following post,