Firstly, there is the New Posts option under the Quick Links drop-down near the top left corner:
If you're looking for the control panel, it's under your user name near the top right corner:
You can see your Private Messages there, and the Control Panel.
One thing you may care to use the Control Panel for is to change your time zone. Somehow we didn't transfer the time zone across with other user information, so you'll be defaulting to London time (UTC). To change it, select User Control Panel from the drop-down as above, and select the Board Preferences tab:
It's pretty obvious what to do from there.
When it comes time to add an image to your post, if you're using the Chrome browser, the not-so-obvious thing you'll need is this, near the bottom left of the post's main edit window:
[ Edit: it seems that Chrome only shows the "hamburger" at certain zoom levels. ]
Clicking on those stripes will switch from Options to Attachments. On Firefox, the tab is already called "Attachments".
From there, click "Add Files" and it's pretty obvious. You can also do this by simply dragging and dropping your file into the post editor. Usually use "Place inline" for images (though you might want to keep a large schematic as an attachment), or leave other files as an attachment. You can inline other files if you want, like this: Remember that [size=xx] is different now; [size=1] is unreadable, because it's a percentage. So for small text, use [size=85] or so. For large text, [size=150] is pretty big. You can get these, and other sizes, from the "Normal" menu in the post editor.
Hopefully, that should get us started. Feel free to add other tips to this topic, but I'd like to keep the chatter to a minimum.
[ Edit: Added info about [size=], where to find the attachment stripes. Attachment stripes issue only for Chrome browser. Simplified the [size=xx] part. ]
[ Edit: Placed the two "Attachments" images side by side. Added info about dragging and dropping attachments, and using "Normal" menu to change text size. -- weber]