Choose File ▸ Place… (Ctrl+D) and pick a file; click on the page to place it, or drag a frame. Turn on Show Import Options to set the import options first.
Hover the image and drag the round content grabber in the middle. Object ▸ Fitting fits the content to the frame (Ctrl+Alt+E), the frame to the content (Ctrl+Alt+C), fits the content proportionally (Ctrl+Alt+Shift+E), fills the frame proportionally (Ctrl+Alt+Shift+C) or centers the content (Ctrl+Shift+E).
Window ▸ Links (Ctrl+Shift+D) lists every placed file with its page and status. Relink, Update Link and Go To Link are at the foot of the palette; a missing link shows a warning badge.