Anyone wanting to learn about SQL Server could do a lot worse than start taking a Udemy course. This is the first of about five. This course is actually one designed for those interested in taking a SQL certification exam.
https://www.udemy.com/microsoft-sql-server-2012-certification-70-461/
It does ask you to download a review copy of SQL Server 2012 which is time limited and that could limit your time studying with an actual copy but still very useful.
The principles behind MS Access are almost exactly the same as SQL Server syntax just thinkg of it as a less friendly UI.
Regards SQL - SQL is a language like VB or C# - it however concentrates on Algebraic manipulation of data - it has standards which vendors are supposed to adhere to. SQL Server uses a version called T SQL while Oracle uses P SQL. MySQL and Postgres probably have slightly other variations.
SQL Server is Microsofts implementation of enterprise grade database engine which you can query using SQL.
SQL the language forms the basis of almost all database engines including MS Access. Many simple queries written in MS Access will transfer straight into SQL Server.
SQL Server has some different data types from MS Access and different ways of setting up things like indexing and autonumbering. A day of instruction for someone starting off is probably recommended after that you are probably off and running.
One difference between SQL Server and MS Access - SQL Server is a server it runs constantly in the background providing data on a machine unless you specifically ask it to stop. You connect to SQL Server using separate clients - the client used to manage databases within SQL Server is called SSMS or SQL Server Management Studio. Each version of SQL Server has its respective version of SSMS. You open up SSMS and then you connect to a server. Each server is called an instance. Another way of connecting to SQL Server is via MS Access which you do in a similar way to the way in which you link an access database to a access database with tables. SQL Server engines are set up as instances where an instance is a collection of databases. SQL Server is very granualar and has lots of configuration options - so many that's where the consfusion comes in. There are multiple ways to do the same thing in SQL Server as well.