I would recommend starting with online tutorials for Analysis Services and online tutorials for MDX. You cannot get much better help for free.
Microsoft SQL Server 2008 MDX Step by Step is the best book I've read regarding learning MDX queries when you are just starting out. It was as good as SQL queries for mere mortals, but for MDX.
Microsoft SQL Server 2008 Step by Step - , , . , , . MDX.
Microsoft Data Warehouse Toolkit, , . Microsoft Analysis Services 2005 Microsoft Business Intelligence Platform , MDX, MDX Step by Step.
Googling MDX , , , . !