What is the difference between a solution and a project in Visual Studio, and how do I open multiple projects?

Question

C++ / C#

Learning C# in Visual Studio
Created a new Weather_bot project and wanted to open an existing Demo, but it suggests either closing Weather_bot or adding it to his solution. From here questions:
- What is the difference between a solution and a project?
- Is it possible to open projects separately just in different tabs (not in the same solution)
- And why are all the tabs called Program.cs? Shouldn't there be a project name?
Here is a screenshot: prntscr.com/it7mjc

Answer 1

1. The solution contains several projects.
2. You can open projects separately if you copy them to a separate folder, but the studio will still create a solution for such projects.
3. Tabs are named after the file whose text they contain.

Answer 2

1) A solution is a set of projects. So it is more convenient to solve dependencies and at the same time divide into modules. Extremely important for large projects.
2) You can. Two copies of VS. Within the framework of one copy, in my opinion, you can only keep 1 solution.
3) The tabs are named the same as the files are called (suddenly!) Why exactly Program - well, because the developer decided so.