Irish Ancestors

I thought that by starting working on my family tree that it would be easy....... Yeah right how wrong was I????

I need some help with Irish Ancestors so if there is anyone that can assist me I would be eternally grateful.

My Great Grandad was a Michael McCann and he married Ellen Dunne in July 1920. However he was married before and I cant find anything at all. Michael's father was William McCann and Ellens Father was Michael Dunne.

If anyone can help me at all.

Thanks

Paul