There are several keystrokes and button events referring to an object without identifying its type. Here's a list of them:

<Btn1> creates (or deletes) an object depending on the current mode.

<Key>BackSpace or <Key>Delete removes the visible object at the cursor location. When more than one object exists at the location, the order of removal is: via, line, text, polygon and element. The drawn layer order also affects the search - whatever is top - most (except elements) is affected before lower items. Basically all this means that what is removed is probably just what you expect. If for some reason it isn't, undo and try again. Only one object is removed for each keystroke. If two or more of the same type match, the newest one is removed.

Use <Key>s and Shift<Key>s to change the size (width) of lines, arcs, text objects, pins, pads and vias, or to toggle the style of polygons (whether pins and vias automatically have clearances).

<Key>n changes the name of pins, pads, vias, the string of a text object, or the currently displayed label of an element.

<Key>m moves the line, arc, or polygon under the cross hair to the active layer if it wasn't on that layer already.

<Key>u (undo) recovers from an unlimited number of operations such as creating, removing, moving, copying, selecting etc. It works like you'd expect even if you're in the midst of creating something.

Shift<Key>r restores the last undone operation provided no other changes have been made since the undo was performed.

<Key>tab changes the board side you are viewing.

For a complete list of keystrokes and button events see Translations.