discrete mathematics - Modular arithmetic for a beginner

I am a student who is struggling terribly with Discrete Mathematics 2. I've already changed my major from computer science to IT because it's just not a great fit for me but I'd still like to leave this course with some knowledge seeing as I've spent a great deal of money on college to begin with.

I am having trouble understanding modular arithmetic and I have to solve these two problems by hand:

$$89 ^ {307} \bmod 713$$

$$49 ^ {307} \bmod 713$$

If anyone could show me how to even approach this I'd be thankful. My class is learning through theorems which isn't helpful at all. I need this to be broken down like it's being taught to a 3 year old. Thank you for your help in advanced.