I have a pool light junction box next to my house and am wondering if I can tie a GFCI plug into the junction box. I have tried but have come up unsuccessful. I am wondering if this is possible and how to get it done properly.

Info:

In the junction box there are two white wires connected to each other
There are also a black wire and blue wire connected to each other
Then there is the obvious green ground wire.

I have pictures but cant seem to post them.