Q: Merging Apple ID and passwords on all devices

Hi, how do I use my Apple ID and password on all my devices? I changed them all on Saturday and it worked but today they have all reverted back again. Now one of my iPod's can't download anything and I cannot login to the AppStore at all because that? Any advice would be greatly appreciated. I am disabled and live alone, my devices are all in different rooms of a double story house. I'm not able to run around and do it all again by myself. I just don't understand how it was all synced and working and now it's not. Thanks in advance, beth