I'm brand new to Mac Book Pro and have used PC's for years. So this may be a stupid question. Using Finder I can copy/paste files from my flash drive to the Mac, but I cannot copy from my Mac to the flash drive. Why?
Your flash drive is probably formatted to NTFS which Macs can read but not write to. If you reformat it to FAT32 then both Windows and Mac will read from and write to it.
Your flash drive is probably formatted to NTFS which Macs can read but not write to. If you reformat it to FAT32 then both Windows and Mac will read from and write to it.
Open Disk Utility (in Applications/Utilities). Select the flash drive in thesidebar (the top entry for it). Click on the 'Erase' tab in the main pane. Type a name in the 'Name' field. Set the Format to 'MS-DOS (FAT)'.