@Emna Sellami raised a good question about moving parts around in xStudio. 

I guess the discoverability issue may arise from several factors: 

1. Remember to double click a part to select it. Single-click selects the entire assembly, rather than the target part. 
2. Once a part is selected, please look for a small triad, sometimes at a corner, as shown below. This small manipulator integrates lots of controls to move, rotate, and scale parts. 
   1. The arrows translate a part in xyz directions. 
   2. The planes move parts along that planes. 
   3. The quarter circles rotate them. 
   4. The top dot to scale up and down. 
3. Hence the click has to be very precise on the triad. 

E.g. 

Drag an arrow to translate: 

Drag a plane to move along that plane: 

Drag the quarter circle to rotate: 

Drag the top dot to scale up and down.  

Now what if I made several unwanted manipulations? 

No worries. You can cancel all these by simply remove all the scene changes as shown below: