you can change the viewport by using the numpad 7,1,3 (top, front, side)
You can also split the screen into more than 1 window. do this by going to the edge of the viewport at the top. when the cursor turns to a little double arrow, right click and select split.
There is a script to convert .3ds files to .blend files. You need to have python installed to use it.
That would be the middle mouse button. click and hold, then use mouse movements to change the view. If you don’t have a middle mouse button there is a way to emulate it but I don’t recall off the top of my head what buttons to hold down while moving.