Suppose you have a Windows machine with a bunch of files on it, and you want to move these files to your Mac.

Many kinds of files can just be copied from a PC to a Mac, and opened and used without any conversion or fixing. This  Apple Support Article describes how to move data. Here are some options:

• Write a CD or DVD with the files from the Windows machine, and read it on the Mac. If your Windows machine will burn CDs, this is the best way to go. It gives you a backup copy of your data too.
• If your Windows machine has networking set up and a file share defined, connect the two computers with an Ethernet cable, or connect both computers to your home network, and then
  • In the Finder on the Mac, Choose Go ► Connect to Server
  • Enter the PC's workgroup name, user name, and password
  • Drag files from the PC window to a Mac window.
• Upload the files from your Windows machine to a file server. Then download them to the Mac.
• Attach your Windows files to E-mail messages from your Windows machine. Read the mail on your Mac and save the attachments.
• Buy Move2Mac and use it.

Mail messages require special handling, depending on where your mail is stored and in what format.