If you are looking to deploy your SSRS (SQL Server Reporting Service) reports directly from Visual Studio you will need to set the Target Server URL in the Properties of your project in the deployment section. The trick here is that this is not the URL for your Report Manager. What you are in fact looking for is the virtual folder where your reports are deployed.
For a standard installation this would be your SSRS server name followed by "/reportserver". For example, if you get to your report manager using the URL http://devssrs/Reports/ you would use the URL http://devssrs/reportserver/. To test whether this is the correct location you can enter the URL in your browser and you should see a page which looks something like this:
If for some reason you do not see this page then it is likely your report server was not installed with the default install. Never fear! Take a look at the quick article which explains how to find the report server name.