There's so much it's hard to know where to start. First, unlike Access, you can't build a front end application in SQL server. YOu will have to use your Access one or build a new one.
A new thing you won't be used to are stored procedures. SQL server uses them to store the code to run queries and more. If you continue to use your access front end, you'll want to convert your Access queries to stored procedures and call the stored procedure to improve performance. Triggers are also new but you can probaly wait alittle to learn them.
Data types are simliar but somewhat changed and you need to learn what equates to what (I had a cheat sheet for the first couple of months.)
In Access you could get away without security and usually relied on network admin for backups. Now you need to learn about these subjects. Pay rapticular attention to roles and transaction log backups. You probably also need to learn about jobs ans alerts.
I'm presuming you are moving to SQL Server for improved performance and ability to store more records. In this case you need to go ahead and set up for performance now while you are doing the initial set up. If you have the hardware. set up your transaction logs and indexes on separate drives with separate drive controllers (different partitions won't be the help in performance that physically separate drives are). Also set up a development server, so you aren't developing on your production database.
If you are a typical Access user, you developed your queries using the graphical interface. If so you may not be very familiar with SQL itself. Access also uses SQL, but a differnt flavor so if you are familiar with Access SQL, learning T-SQL will not be too bad. If not, well you probably need to get a good book on stored procedure programming and/or the T-SQL language.
SQL Server comes with Books Online (known as BOL around here) which is a good reference to all the commands, but somewhat intimidating to the beginner. Also you do kind of have to know what you're looking for to find things.
There's more but this should get you started. I'd run down to the local bookstore and get at least one book on SQL Server admin and one on stored procedures or T-SQL.
But take heart, a lot of us came from the Access world and we all have survived, so you can too. Just be prepared to learn a lot of new ways to think about things.