Hi BK. I use my iPad for storing all my songs used an APP "GoodReader for iPad" which I believe was free. I find transferring songs from my Mac quite easy, I also keep a copy of someone else singing the songs I song, just to remind me of the tune. I use my iPad when I sing as I have a problem with memory, which according to the medical profession will not get better but will get worse, obviously if I need to listen to the tune this is done well before I sing. There is as previously mentioned "Songbook" which has a couple of advantages if you need them, which I don't. These are that you can get the words to scroll at a speed set by yourself and you can obtain music and keys etc to assist, useful if you accompany yourself on an instrument.
Hope this is helpful and good luck.