To  To align two parts by selecting three points:

1. Right-click on the part you want to move.
2. Now select Align....
3. Select a point from the selected model.
   
4. Select a respective point on the second model to align the first point on the first model.
   
5. Select a second set of points similar to the first to align the models more.
   
6. Finally, if needed, select a third set of points to completely align the two models.
    

 To align two parts by selecting an arc and a point:

1. Right-click on the part you want to move.
2. Now select Align....
   
3. Select By Arc and Point from the Align Items dialog box.
4. Select an arc on the first model.
   
   
5. Select a respective arc on the second model.
   
   Use the Flip Axis button to align the other side of the arc if not correct.
   If the models are aligned, click the Stop button. Otherwise, continue to the final step.
    
   
6. Select respective points from each model to finish the model alignment.