Do the following mentioned exercises at a table that supports your forearms.

One Two Three Finger Exercises
For the best results possible, you should be able to touch the tips of your fingers to the palm and you would be able to straighten your fingers in a proper manner. Use the one-two- three approach in order to go on with the exercise procedure:
To bend fingers:
Begin bending the joint closest to the tip of the finger
Then bend the middle joint
When your fingertips are touching the palm, or even they are at their maximum on touching the palm, then bend the knuckle joint.
To straighten your fingers, make sure that you perform the movements in reverse. Follow these steps(3,2,1)

1. First straighten the knuckles
2. Then the middle joint , and
3. Straighten the fingertips.

You can exercise your fingers individually or together, but if you are a beginner, or of the problem is too severe, then make sure that you don't add too much stress.

Thumb

Walk

1. Holding your wrist straight.
2. The next step is to form the letter "O" by lightly touching your thumb to each fingertip.
3. After each "O" straighten and spread your fingers.

Make sure that you do this from one hand and use the other one in case of need.

Hi and By

1. Rest your forearm on a table with your hand over the edge.
2. Keep fingers relaxed and don't stress them too much and then bend your wrist up and down.
3. Slide your arm back till the time you find that your fingers hang over with your knuckles at the table edge.
4. Don't bend your fingers and keep them as straight as possible and together and your palm flat.
5. Now move your fingers up and down.

Door Opener : this exercise will make your stiff hands a little flexible, so that you can carry on with your day to day tasks.

1. Start with your forearm... Rest your forearm on a table, palm down.
2. Keeping your little finger on the table.
3. Now turn your hand so the palm faces up.