On the left handside at the top there are the words "Compose" and "HTML". "Compose" is for normal typing, HTML shows you the computer language for what you are writing - you don't normally have to worry about that tab, just type in "Compose"mode.
Add a title for the post at the top of the window.
Click in the white box and begin typing your message.
You can highlight the text to change the font, size, appearance etc.
You can insert a web link to another web page using the "Link" tool.
If you wish to insert a picture or video click on those images in the toolbar and follow the instructions it gives you.
You can align the text, add numbers or bullet points as you wish.
On the right hand side toolbar you can see the work "Labels" Click on that and add 2-4 words that would best describe the topic of your post. These separate words would enable searching for your blog more easy. For this post I would use labels like blogging, Oaklands, Post. If it is a child authoring the post have them put their christian name as a label. This will enable parents to view the posts authored by their children more quickly. They should be separated by commas and are usually individual words.
A list of post labels will appear on the side bar of your blog. Click on a label and you will be taken to the relevant posts. It is like a mini search engine for your blog.
When you are happy with the appearance of your post click publish.
Click on "View Blog" to see if it is what you want.
If you need to change anything hover the mouse over the name of the post in the post list and click on "edit", or click on the pencil icon. Go through the steps above to alter it.