I want to add solution to source control(tfs I am using vs 2015).I selected the option add solution to source control, then one dialog opened, in that dialog there is no option to create a new folder directly under collection, it is always adding to the existing project(folder).How can i create a new folder/project directly under the collection.
The structure TFVC uses for source control is as follows:
You can't add source code directly under a Team Project Collection -- it has to be created in a Team Project. And you can't just create a "folder" that represents a new Team Project. You have to create a Team Project either via the web UI (if you're using TFS 2015 Update 2 or later) or via Visual Studio. The version of Visual Studio used to create a Team Project needs to match up with your version of TFS, as well.
Typically, guidance for Team Projects is to create a single team project for each portfolio of related applications, since each Team Project is isolated from other Team Projects in terms of things like source code, build, release, and work item management. You can use the concept of Teams within a Team Project to create separate backlogs and the like for individual applications.
Some further reading:
Why you should use one Team Project: http://geekswithblogs.net/Optikal/archive/2013/09/05/153944.aspx
Creating a team project: https://learn.microsoft.com/en-us/vsts/accounts/create-team-project