Where to start to understand a unknown database

So, the title sums it up.

I've got a SQL Server database with 28 tables and 86 stored procedures that must be reverse engineered. I'm pretty sure that some tables are never used and that not all procs are used as well.

The biggest problem is that all the Windows Services that were created to be used with this DB and all the software and database documentation is lost, and the person that designed the whole system is nowhere to be found.

I've already managed to create an ER diagram to help me understand the relationships, but as I am not experienced in database administration, I have no idea where should I start.

Also I'm sorry if this kind of question is not meant to be asked here.

Your best bet to start is to document your database using SQL Power Doc

SQL Server & Windows Documentation Using Windows PowerShell

SQL Power Doc is a collection of Windows PowerShell scripts and modules that discover, document, and diagnose SQL Server instances and their underlying Windows OS & machine configurations. SQL Power Doc works with all versions of SQL Server from SQL Server 2000 through 2014, and all versions of Windows Server and consumer Windows Operating Systems from Windows 2000 and Windows XP through Windows Server 2012 R2 and Windows 8. SQL Power Doc is also capable of documenting Windows Azure SQL Databases.

Note: I have used it and it will give you a really good start in documenting and understanding your database server instance.

StackExchange Database Administrators Q#124082, answer score: 7