A solution is generally a collection of one or more projects. Opening a solution file will tell Visual Studio to load all of the related projects. A solution file has the file extension .sln. There are a few ways to open a solution'
Method 1. Go to the folder that contains the projects and double click on the solution file. Visual studio will open and load the solution.
Method 2. Open Visual studio and select the option to open a project or solution. Go to the folder that contains the solution and click open.