You can immediately start using AVAST32 if the installation of the program is successfully completed.
The installation program has created "AVAST32 Antivirus" folder for you (if it hasn't been changed during the installation) containing "AVAST32" shortcut. The created folder is situated in the menu of the "Start" button (it shall be displayed after clicking on this button by the left button of your mouse), in the "Programs" folder.
The form of the menu of the "Start" button depends on the setting of your operating system and on the programs installed so far.
So for starting the AVAST32 program click on the "Start" button, then select "Programs" folder, search for "AVAST32 Antivirus" folder and in this folder click on "AVAST32" icon.