In Flash two types of tweening is possible - Motion tweening and Shape tweening.

Motion Tweening: Motion tweening is used to tween the changes in the properties of instances and other objects. With motion tweening we can change the position, size, rotation, and skew objects to create motion from one frame to another frame. Additionally, we can also tween the color of instances, make the color to fade in or fade out. To tween the color of any object we must convert them into symbols. See Creating symbols for that. 

We can create motion tween by using the steps below:
1. Open a new file by clicking File and selecting New. 
                          File > New
     A layer will already be there with a blank frame. First name the layer as "Motion Tween". Select the layer by clicking on layer name.
2. Now draw a object using toolbox or drag and drop an instance of a symbol that is 
    already in the library on the stage. Now the object will also be in the first frame of 
    the layer. Don't forget to convert the object into symbol if it is not a symbol already. 
3. Insert a frame on the layer, upto which point u wanted the animation to last, by 
    clicking Insert and selecting Frame.
                         Insert > Frame 
    or by right clicking ( for Windows user ) on the point of interest and selecting Insert 
    Frame.
4. Select the first frame of the layer. Click on Insert and select Create Motion Tween
                    Insert > Create Motion Tween
    or right click ( for Windows user ) on the frame and select Create Motion Tween.
5. Click on last frame and insert keyframe by clicking on Insert and selecting
    Keyframe.
                        Insert > Keyframe
    or right click ( for Windows user ) on the frame and select Insert Keyframe. Now the
    the layer should look like as shown below. Here I have created an  animation that 
    lasts for 20 frames.

6.  Now select first frame and set the properties of the object as you want them to 
     be in first frame. After that select the last frame and make changes in the 
     properties as per you wanted the animation to look like in the last frame.

     The properties that can be changed to create an animation are:
1.  Position: We can change the position of the object at particular keyframe just by
     repositioning the object on the stage at that particular keyframe. Select the 
     keyframe and drag the object to the desired position.
2.  Scale or Rotate: We can change the size of the object in particular keyframe to 
     create zoom in or zoom out kind of effect. To change the size go to Modify then 
     select Transform and click Scale.
                                Modify > Transform > Scale

    We can also make the object rotate by using the rotate option. Select the keyframe
    in which you want the object to rotate. Go to Modify, select Transform and click 
    Rotate.
                                     Modify > Transform > Rotate.
    Windows user can right click on the object in the particular keyframe and can
    select the Scale or Rotate option.
 

Right click Scale option	Right click Rotate option

3. Color Effects: We can create few color effects on the objects in Flash and we can 
    use these color options to create color tween. To use these options go to 
    Windows, select Panels and click on Effects. The window will be as as shown 
    below.

                                 
    We can use five effect options Brightness, Tint, Alpha or Advanced option. Select 
    the keyframe on which you wanted the color property of the object to get changed. 
    Now open the effect window and select one of the option. You  will get few more 
    options on the window and by changing them you can get the desired effect. 
    Suppose you choose Alpha effect.You can see the change in window as shown 
    below the effect window. You can change the percentage value and can get the 
    desired effect. The same can be done with Brightness. With the help of Tint 
    we can change the color. With the Advanced option we can change color as well 
    as Alpha. Make sure before using the effect options that the object is a symbol.
Motion Tweening along guided path: We can create motion tweening along a user 
define path.For defining the path along with you want the object to move follow the steps written below:
1. Do first three steps as we have done while we were creating simple motion 
    tweening.
2. Now insert a Guide Layer. Guide Layer is a type of layer, where you can draw a 
   desired path for your object to move along. The beauty of the Guide Layer is, it will 
   not be visible in the actual movie. We can see it on the stage while we are creating 
   the movie. To insert the Guide Layer click on the icon   at the bottom left corner 
   of the timeline window. Alternetive way is go to Insert and click Motion Guide.
                               Insert > Motion Guide
3. While the Guide Layer selected, draw a desired path on the stage using Pencil 
    tool or Line  tool from the Tool Box.
4. Select the layer of actual object and create motion tween using step 4 and step 5 
    of motion tweening. 
5. Place the object at the starting point of the path in first frame and at the ending 
    point of the path in last frame. Now you have created the motion along desired path.
Shape Tweening: Shape tweening is used to tween the shape of  instances and other objects. With shape  tweening we can create the effect of transforming one 
object into another object. Due to tweening we just need to define the object in first and last frame of the animation. We do not need to worry about the intermediate layers. To shape tween the object we must convert them into symbols. See Creating symbols for that.