Your applications must be deployed to be used. Deployment options have varied over the years. All have had advantages and disadvantages, and they have evolved to meet the needs of a given era.
Older deployment options are still available for applications based on .NET Framework 4.5, and you can continue to use those options for server and desktop applications. Those include xcopy deployment, ClickOnce, and creation of .msi files. There are also third-party products that package and install applications. Most experienced developers who use Microsoft technologies are familiar with one or more of these options.
Changes in the last few years have highlighted some disadvantages of these older options. In particular, the most common way to acquire applications has changed from inserting physical media into a computer to downloading applications straight from the Internet. While this certainly simplifies buying and installing applications, it also opens up computer users to a serious threat: having deployment mechanisms hijacked by malware.
Estimates of the cost of malware go into the billions, and the problem is rapidly getting worse. Malware authors have shifted to attempting to acquire information and credentials to manipulate financial accounts, which threatens to dramatically inflate the damages due to malware.
One model that has evolved over the last few years to address that problem is the “app store.” Many users will be familiar with ...