Subversion has its own command-line client. Other clients are available, which are perhaps easier or more intuitive to use in different scenarios. Often, people have several clients installed, and use each for different tasks.
Tortoise SVN is a Windows shell extension, which gives feedback on the state of versioned items by adding overlays to the icons in the Windows Explorer. Repository commands can be executed from the enhanced context menu provided by Tortoise.
Some programmers prefer to have a client integrated within their development environment. Again, visual feedback of the state of versioned items is provided, and repository commands are added to the menus of the development environment. Examples of this approach are AnkhSVN and VisualSVN for use with Microsoft Visual Studio, and Subclipse for use with Eclipse.
It is common to expose Subversion via Webdav using the Apache web server. In this case, any Webdav client can be used, but the functionality provided this way is limited.
