Activating a Script (Newbie Question)

I have been reading through the forum but still have a really fundamental scripts question.
I now know where to place scripts in the content of an object I create but I cannot figure out how to activate the script.

I was trying to use the Basic Pet Script (Follow/Face Owner) shared by Logan Bauer earlier in the library. But how do I get it running? Should my avatar touch or take the object which has this script associated with it? Do I need to input my avatar's name into the script somewhere? How can I get the scripted object to react to my avatar and follow it?

Thanks in advance for your help.

Here is Logan's script for reference:

////////////////////////////////////////////////////////////////
// Open Basic Follower/Facing Script, by Logan Bauer. //
////////////////////////////////////////////////////////////////
// OFFSET is the position of your pet in relation to it's owner's position.
// For example, in the default setting below, "vector offset =<-1,0,1>;"
// I.E. (x,y,z), the -1 puts it 1m back behind owner, the 0 means don't have
// it stay left or right, and 1 means have it stay 1m above it's owner.
// So, if you wanted the script to make it follow directly in front of you,
// and to the left, then you would change it to "vector offset =<1,1,0>;"


vector offset =<-1,0,1>;

startup()
{
vector pos = llGetPos();
llSetStatus(STATUS_ROTATE_Z,TRUE);
llSetStatus(STATUS_PHYSICS, TRUE);
key id = llGetOwner();
llSensorRemove();
llSensorRepeat("",llGetOwner(),AGENT,200,2*PI,.5);
}

default
{
state_entry()
{
startup();


}

on_rez(integer start_param)
{
startup(); }

sensor(integer total_number)
{
vector pos = llDetectedPos(0);
llMoveToTarget(pos+offset*llDetectedRot(0),.3);
llLookAt(pos, .1 , 1);
}
}