I am beginner in field of opendaylight and mininet. I want to know about restconf and rest.
The idea behind REST is that, rather than using complex mechanisms such as RPC to connect between machines, simple HTTP is used to make calls between machines.
RESTCONF is a REST like protocol running over HTTP for accessing data defined in YANG using datastores defined in NETCONF. It listens on port 8080 for Http requests and supports OPTIONS, GET, PUT, POST, DELETE operations.
In the case of Opendaylight, you can use REST clients (plugins on browsers) to perform these operations in the northbound interface of ODL.
For example, if you have a mininet topology controlled by an ODL and would like to add flows to the switches there, you could use the "PUT" operation to do the same by referencing the right URL.