You can create and edit blog posts by going to "Posts" in the left hand menu:
Here you can create a new post directly in the Posts folder, or browse to a sub-folder and create the post there. You can also create new folders on this screen. This is done by clicking on the "Create new" button and then choosing either "Post" or "Folder". I like to group my posts into sub-folders by year. You could also add month sub-folders if you write many posts.
When you create a new post, you will see the following screen:
Towards the left are some properties you can configure for the post. The post title, the date to be used for the post and the tags you wish to assign to the post. These are all fairly explanatory. Note though that the date-time selector has a problem with the time and you might struggle to pick a time in the afternoon. Unfortunately this is an issue in Forestry.
On the right hand side of the screen you can write your post content. This is a basic WYSIWYG editor with some styling functionality listed at the bottom. The content is stored in markdown format. You do not need to know markdown to use the WYSIWYG editor. However if you wish to edit the markdown generated by the editor, you can use the three vertical buttons towards the top right to switch into "Raw editor" mode. Markdown is a more user friendly way of writing HTML and you can find out more about writing in markdown here. You can also click on the keyboard icon at the bottom right to bring up a quick reference guide at any point.
If markdown doesn't provide the functionality you need, you can also add HTML into the raw editor. Tables is one content type you will need to use HTML for.
Whilst editing your post you can click on the preview icon at the top right to see a live preview of your post at any time. There is no need to save your content first. Just click the preview icon to update the preview.
Once you are done editing the post content you need to save it using the "Save" button at the top right. This will save your post so that it is ready for publishing - it will not make your post live. In order to publish the post as soon as you are ready, follow the instructions in GitHub: Step 4 - build and publish your site. Alternatively the system will automatically rebuild your site at midnight every day, so you do not need to manually update the site if publishing the post can wait that long.