MDX measure to DAX conversion

I needed a little help on working with MDX and DAX. Recently I have just started working with these two terms and am having a little trouble figuring out the differences and possible examples of how they work. The articles I have read online are giving me a little trouble and I am finding it hard to understand. It would be great if someone could, maybe, kindly explain it in simple words what they are and what they do? Thank you so much for the help!