1 - Writing in a Board
To write in a Board, all you have to do is select the "text tool" in the toolbar (bottom left), symbolized by
.
You can then click on the Board directly, in the whished area.
Format with available text options
2 - Connecting elements together
To link two elements together (idea, shape,...), you will just have to select the "link tool" in the toolbar (bottom left), symbolized by 
.
Then click on the idea, starting shape, hold your click and extend your link to the other idea/shape.
By clicking on your link again, you will be able to modify it, format it, choose its color, etc...
3 - Lay out your Board
To lay out, we invite you to check out this article on aligning ideas.