Hello and Welcome to SP!
To enter a blog, you have to click on EDIT your page...then it will let you add a new blog entry :)
If you go to your sparkpoints page, and scroll down to post a blog entry, it will take you right to it! :) You also need to have a sparkpage set up.
Holler if you need anything else. Don't worry about numbers on the scale or clothing sizes...worry about how healthy, fit and strong and how much energy you have! :)