First add in ID column to your database if you have not already done so. Make this the primary key by clicking the key icon. Then in the properties section at the bottom find identity and set it to yes. The seed is the starting number you would like. for example if you want your first id to be 1000 put that in the seed. the default is 1. Also in the increment put in the number you want your id to increase by with every entry. Default is 1 again. so this will increase your id from say 1000,1001,1002 etc.
When you save data to the table the id is created automatically and you do not need to do anything to calculate this yourself.
If you require to show the id on screen you will need to create a stored procedure to do the update and return
which will be the id value of the last created record.
Create Procedure InsertUser
@address varchar (50)
insert into MyUserTable(name, address)