Adding text is still not fully supported unfortunately, although it has been requested a few times!
You can add a text box on your plot but it's not very customisable.
You can label a pipe or truss quite easily though. Select it and you will see in Selected Item properties you can give it a Unit name, and under Plot there is annotation and dimension. This will create a label which you can move around in the Paper view by double clicking on it to select. The only annoying thing is that for a truss this will put a label on each individual piece of truss, even if you have grouped them. And as you can't delete any of them, if you want one label to the side of each truss, rather than four or five labels spaced out on your truss getting in the way of the lights, you have to carefully drag them all on top of each other or way off to the side!
Thanks for reminding me of these little niggles I have with Capture! It's great software, really, and the guys are always making it better. There are just a few funny little quirks that need to be tidied up so it's good to point them out ;-)