Hii Suyash,
For callouts, Apex only supports the document literal wrapped WSDL style, along with primitive and built-in data types. Some of the used tags used in WSDL are as follows:
<types> – Defines the (XML Schema) data types used by the web service
<message> – Defines the data elements for each operation
<portType> -Describes the operations that can be performed and the messages involved.
<binding>- Defines the protocol and data format for each port type.
Thanks.