Can anyone please explain me what are the functionalities of software testing.
I think you might need some correction with the question. The right question should be asking about the functionality testing aspect of the software testing which is checking any application or software for all the functions it is required to offer.
Yet, if from functionalities you wanted to know about the purpose of objective of software testing, it can be explained as testing the core application functions and anything that might affect the user experience and security. For instance, an eCommerce app is usually tested for text input, menu functions, installation, ease of navigation, load on the device, security of payments, data storage testing, and anything that makes an application offer seamless experience to the end-users.
In case, you are looking for something else, please provide a little more detail on your query and I would like to answer you.