SQL (Structured Query Language) is Language used to maintain and Save data Efficiently. It Relational Data Management system mainly developed on SETS concept in mathematics . Microsoft SQL Server is a SQL Server of Microsoft company . It is highly Efficient and Secure Server by Microsoft .
It has different Edition of product for use
it is Students and small developer with no charges (Limitation only 10 GB of data you will be able to store . Many features are not there)
It is Paid version by microsoft. SQL Server Enterprise Edition includes both the core database engine and add-on services, with a range of tools for creating and managing a SQL Server cluster. It can manage databases as large as 524 petabytes and address 12 TB of memory and supports 640 logical processors (CPU cores).
It has many different versions also to know more about it you can visit wikipedia.com. It is here
Steps to setup Microsoft Structured Query Language (MSSQL) Express Edition
Following Video Demonstrate Screens after download and install Process of MSSQL Server Express Edition
Install and Download SQL server Management Studio