Alan, if I think I've read your original question right you're trying to make sure that the text doesn't go right to the edge of the text frame.
If you're wanting this because, for example, the text frame has a visible border and you want to put some distance between the text and border you could look at the "Columns and Text Distances" section in the "Text" tab of the "Properties" window. This, among other things, allows you to set a distance from the top/bottom/left/right of the frame. If you try it you'll see another rectangle appear inside the text frame showing you where this new "inner frame" is.
If, however, you've got text frames next to each other and you don't want the text from one frame touching the text of the adjoining frame, you can just move one frame a bit to the side so they don't touch. In DTP you can put the frames wherever you want them on the page, unlike CSS where the renderer tries to "crush" everything together (making you add padding etc.).
From your second post it seems like you're trying to add a space around an image so that the text around it doesn't touch the image. When I started with Scribus I used the exact same method you've been using. However there's a much better way as mentioned by Nermander.
Create your image frame. Then in the "Shape" tab of the "Properties" window select "Use Contour Line". Then, in the same tab, press the "Edit…" button. This will bring up a node editing window. Check the "Edit Contour Line" option near the bottom of the window. You'll see some "Enlarge" icons near the left-middle of the window and pressing one of them will enlarge the contour line of the image by either a percentage or an amount depending on which icon you choose. You'll notice the blue box around the image get bigger. This contour line is what the text will flow around. You can edit this line more by using the other options in the window but for basic rectangular images you can probably just go for the basic rectangular contour line. Press the "End Editing" button when you're done.
I hope some of this helps.