SQL Server is a database engine used to store data. Unlike Microsoft Access (which can also store data), it does not come with tools to input or display data. That is done via web pages that connect to the database or a program written using a program like Visual Studio by a developer that connects to the database.
The SQL Server program can run many databases. Perhaps one department of your company needs a database for their purposes only. A different department also needs one for a completely different purpose that has nothing to do with the other department.
It's possible you already have it without realising it! SQL Server comes with different versions of Windows Server.
There are different versions:
There is now an alternative to running your own SQL Server software, which is to let Microsoft run it for you!
In order to run the SQL Server software locally you may need to;
All of which could be quite expensive.
Azure SQL Database does away with these problems as it runs in Microsoft's data centres. Your front end programs are pointed to your Azure SQL Database database not your internal one. Of course there are things you need to consider:
But probably the biggest advantage is cost. The pricing starts at £6 per month. Yes it's not a typo - six pounds per month!
We have one customer running out of three sites with an Access front end and about ten users. They are very happy with it.
The Microsoft Azure site has more information, but it can be overwhelming as it's pretty technical!
See also SQL Server Reporting Services (SSRS)
Based in Northampton in the UK and working with companies worldwide.