I am new to use ubuntu version 18.04.1. After installing right click is not working however i am able to use when i use external mouse, But built in mouse is not working. Please help me System Details - Dell Vostro 3446 64 bit architecture.
By built-in mouse, do you mean the trackpad? If yes you probably need to configure your trackpad to right click as you usually do.
To do so you can go to System > Preferences > Mouse > Touchpad
More information here: https://help.ubuntu.com/community/SynapticsTouchpad