How do I put a border around a text box?

I don't think you can put a border on the text box itself. You'll have to put a rectangle around it:

Another option is to flow the text in a box, using Text -> Flow into Frame. First, you have to draw a rectangle , and type some text . After you select both object, you can use the flow function. The benefit is that, when you now resize the rectangle, the text reflows automatically .

[Edit]
You can change the left margin of the text by resizing the text-field itself (when it is already flowed).