As you have just "downloaded" Mahara, I assume you work with Mahara 1.3? You actually do not download Mahara and use it, but an administrator installs it on a server and everybody can access it online. You did not provide any information, but I assume you are a student using Mahara.
Mahara provides you with a blog per default. You do not have to specifically create one. That is to facilitate the beginning of using a blog as reflective journal.
When you want to add a blog post to your blog, you just need to click on "New Post" and fill in the text boxes with a title, your actual reflections / text, and also tags to be able to find your blog post more easily later on.
At that stage, your blog post is only visible to you. You will have to put it into a view to show your tutor. -> Go to "My Views" -> Create a view (or edit an existing one) -> Choose "Blog post" from the tab in the view creation page and drag the block into the content area. You can then choose your blog post for display.
Alternatively, you can make your entire blog visible at once by dragging the block "Blog" into your content area.
Hope that helps.
Cheers
Kristina
]]>