Readied Action and Attacks of Opportunity

I am giving both Hero Lab and d20Pro a trial run to determine if my gaming group will switch over to a VTT for our gaming. We all live in different cities and travel 2-3 hours once a month to game together. We are hoping this will be a better solution. Basically I'm a total Newb to d20Pro, so I might be asking some dumb questions. I've searched the forums and the user guide and didn't get any hits (which I find odd). We are playing the Pathfinder system, but I don't think that matters for these questions.

How do I do a readied action? Say a character readies an attack with his sword until a creature steps into one of three squares in front of him. When I move a creature into one of those three squares how do we interrupt the creatures turn so the character can attack? Also I would assume the character would then be just before that creature in the initiative order going forward.

Now lets say a creature does something to create an opportunity attack. How do I halt the creatures turn and let the player attack? Do I as the Judge have to carry out the attack or can I hand control over to the player for this?

Thanks for any insight.