Can't connect to Database Engine
Creating SQL Server logins is a bit tricky and you need practice to understand what's going on.

There is an excellent article about it here.

In essence you need to consider the "server credentials" as well as the "database credentials". They are both different things.

I would normally run SSMS and go down to the bottom of my server instance where it's showing the Security folder (as explained in the above link). In there, expand it and right click to create a new Login. Set up your LoginID and Passwords, and default the login to the database you're referring to. Next go to Securables, and choose the correct database, along with the Schema, etc.

Once that's done you'll notice the same login was created at the database's Security folder. Make sure you've given the new Login, all the right permissions to READ and/or WRITE to the database.

The reason you need to do what I've mentioned above, is so you have a correct and valid Login to the database, which is important. Creating a single Login directly inside the database's Security is not enough.

Then you can connect to the database from external sources (Excel, programs, etc) in many ways, using the right connection strings.