Hello calu,
to copy and paste content of a document depends on the kind of the content.
You can't select fix positioned (free moveable) objects and inline (move with text) objects at the same time. So you have to copy the text in the main text area of a page and the objects placed in it first. Than you can select and copy all other objects outside of this main text. But be sure you have unchecked the menu item "Format/Advanced/Make Master Objects Selectable", because if you copy them to the new document, they will be normal fix positioned objects and you have to separate them from the normal fix objects by hand.
So you have to copy and paste a page content (if it is NOT the ENTIRE page) in three steps: 1.) The main text area with its inline objects. 2.) The objects for the Master Page. 3.) The fix positioned objects.
If you want to copy an entire page, do it like Gerry wrote above: If it isn't, separate it with one or two section breaks from the rest of the section, select the page in the thumbnail view and use the copy function. Select the thumbnail view in the new document and use the paste function.
So you can copy one column into another document if the column uses not the main text column of the page. The main text area (column) is the middle field you can see by opening a new empty document and show the layout guides (menu: "View/Show Layout").
To answer your last question, you paste the image with the text cursor visible. This means you insert the object as an inline (move with text) object. You can change the state to a fix positioned (free movable) object, by activationg the option "Fixed on page" in the wrap inspector. Or you can insert the object after you have made the text cursor invisible by clicking outside of every text area near the borders of a page. You can see where to click best by showing the layout guides.
If you can't move this object, it may be you have locked it unintensional by hitting the shortcut [command]+[L]. Than it shows gray "x" where normally the rectangular handles are. Unlock it with [option]
[command][L] or the manu item "Arrrange/Unlock".
