There have 3way to save a game.Now I tell 2 Ways.
1st way:
If your android vertion is under 4.4.read below insteraction...
1-Enter a game
2-Click start /play
3-Then you find Game Screen,like this image,

4-There you find 3dot/menu bar/Phone menu,Under screen.
5-Click there(Menu bar/3 dot)
6-Then open a page ,like below image

7-There you find many option,such as ,save,return,menu etc.
8-Click Blank home/blank
9-After click on blank,its look like below image,

10-Its means you have successfully save your games
2nd way-
If your android up to 4.4 you can try it.under 4.4 user also can try it
1-Enter games
2-Click on Games menu

3-Then open a page ,like below image
4-There you find many option,such as ,save,return,menu etc.
5-Click Blank home/blank
6-After click on blank,its look like below image,
7-At last you can successfully save your game
Note-You can overwrite on save games.

