Noob question: How do I rearrange a large equation?

As a basic example

{v = u + at

Rearrange for a.}

I literally cant find the answer anywhere on google, youtube, or these forums. Please bear with me if its a simple question, I only got my teeth into the program yesterday. Its the one function I need to speed things up. I don't want to have to do it on paper every couple of minutes.

Many Thanks,
Ben