With public cloud all services and resources(infrastructure) are provided by cloud providers. Here user just need to have good internet connection, rest everything like Virtual machines, networks, storage space are provided off-site.
Popular examples of public clouds are
AWS - Amazon web services
Among many others.
In simple terms, once user get into his/her cloud login, he will have everything needed for software development (coding, testing, automation, continuous integration and continuous deployment and so many other things which user need). Only difference from in-premise (current way of doing) is that, setup is managed by cloud provider without much control given to user. User just need to pay for his cloud resource usages.