Objects can be moved around by clicking on it with the left mouse-button:
Move an object left or right - Press the left mouse-button, keep it depressed and move the mouse left or right.
Move an object up or down - Press the left mouse-button, keep it depressed and move the mouse towards you or away from you.
Move an object forward or backward - Press the left mouse-button, keep it depressed then press the right mouse-button, keep it depressed also, and then move the mouse towards you or away from you.
Rotating an object - Press the Alt-key on the keyboard and the left mouse-button, keep them both depressed and move the mouse left/ right/towards or away. The total movement into the left/right/towards or away direction controls the amount of rotation. The movement into the left/right-direction will rotate the object left or right, while movement towards or away of you will rotate the object up or down. As you can see this is very difficult to explain so you'll have to experiment a bit.
All objects , except the paintings
which have another way of resizing, can be resized by clicking on it with your
left mouse-button while holding down the Shift-key on the keyboard. Moving the
mouse left will then decrease the size while moving the mouse right will increase
Double-clicking on an object while you're holding down the Shift-key will make the object the default size again. Objects that have the default size are drawn slightly faster.
Select one object at a time by clicking
on it with the left mouse-button while you have the Ctrl-key on your keyboard
If you did that while you didn't select an object you are able to select multiple objects by keeping the Ctrl-key and left mouse-button depressed: A Rubber box appears which defines a square on the screen that can be resized by moving the mouse left/right up/down. If you let the left mouse-button go all objects that were in this square are selected no matter how far the object was away.....
Now, if you want to select only the objects that are reasonably close, you press the right mouse-button also and do as if you are changing the distance of an object (see above). You'll notice that a dark sphere is drawn around your viewpoint, everything that is in this sphere (highlighted) and in the square will be selected.