如何修复服务器错误'/'应用程序?

I've been following this old Youtube video on how to build a website using asp.net and also connecting in MSSQL. Since I have no knowledge yet on how to create back-end stuff, I think it was a good idea to have a format to follow. I copied every code and I ended up having a couple of errors. I just clicked the show potential fixes and chose the first available option. All errors was gone and I was able to run the homepage of the website. But as I navigate through Reviews and then Coffee. I got a Server Error in '/' Application. As much as i want to fix this myself, I don't really have any idea yet on what to change. Hope you can guys help. I've been following this old Youtube video on h