Can someone help me with a Tumblr question?

I have another Tumblog that, at least for now, I’d like to use as a private journal of sorts. I don’t even know what an API really is, but apparently a properly tuned API “script” might be what I’m looking for.

I want to be able to post to this Tumblog of mine, outside of the Tumblr site and make each post private. The goal, to have a private Tumblog Journal of sorts.

Anyone know where to go for help or can offer some help in making this happen?