Incorrect syntax near the keyword 'Exec'
There are multiple issues with your string @SQLString:


You don't require + at the beginning and at the end
A date will not concatenate with a nvarchar without conversion (CAST or CONVERT)
Because your table will contain spaces you need to put the table name in square brackets: [ and ].
You will be better off with exec sp_executesql @SQLString


So your script might work with this:

DECLARE @SQLString NVARCHAR(MAX)
SET @SQLString = 'Create Table [' + CAST(GETDATE() AS NVARCHAR(30))+ '_Table]' + ' (' + 'Column1' + ' ' + 'Nvarchar(50) Null' + ')' 
PRINT @SQLString
-- Exec sp_executesql @SQLString


I'd recommend reading up on the CREATE TABLE statement and on the String Functions. Then carry on to the Data Type Conversion documentation and have a glimpse at the sp_executesql syntax.

Good Luck.