I am new at using TFS online and creating projects. When creating a project on TFS online platform, and connecting from Visual Studio, I need to map the project on my disc. And I see a workspace that has the same name as my computer. Does Visual Studio create a workspace on Visual Studio for every TFS project? What is the goal of workspaces?
A workspace represents a mapping between a location in source control ($/SomeTeamProject/SomeFolder and a location on your computer (C:\SourceCode\SomeTeamProject\SomeFolder).
That's all. It's a very straightforward concept.
You can maintain multiple workspaces for purposes of isolation, or just have one workspace mapped to the team project collection root ($/), which means that every team project in the collection will be mapped in the same workspace. It's entirely up to you. The advantage of multiple workspaces is that you can explicitly avoid doing things like modifying a bunch of stuff across branch or team project boundaries inadvertently. If you have a workspace for a development branch, you'll only be able to check in a set of files in that branch. If you want to check in files in another branch, you'll have to switch workspaces. It can be a nice sanity check, but it's by no means a necessity.
Workspaces can consist of multiple mappings (for example, $/Foo/Bar -> C:\Foo\Bar, $/Foo/Baz -> C:\Foo\Baz would map those two folders, but ignore any other folders under $/Foo).
Workspaces can also contain cloakings -- explicitly excluding a folder from being mapped. So you could map $/Foo/ and cloak /$Foo/Bar if you wanted everything under $/Foo except the Bar folder.
Workspaces come in two flavors: Server and Local.
Server workspaces were the default from TFS 2005 up until TFS 2012. In a server workspace, every activity you take in source control has to happen through Visual Studio (or an equivalent IDE) -- starting work on a file contacts the server and checks the file out. Files are stored in the file system as read-only unless they're checked out.
Server workspaces are, generally speaking, awful. I do not recommend using them except for in a few very specific cases.
Local workspaces were introduced in TFS 2012 and were first supported (not surprisingly) in Visual Studio 2012. Local workspaces are slightly more Git-like in that editing files does not require an explicit check-out on the server -- you can edit a file at any time in any IDE. This allows you to work offline in a very limited fashion.