Bubbles are one of the easiest things to create in Photoshop. Here's a quick tutorial on one of the methods I use.
Start with a blank page and fill it with light, baby blue color. Now make a new layer to make your bubbles on. Select the Circle Selection Tool with no feather and make a medium sized circle in the middle-upper left hand area of the page. Then, while holding down Shift, make another smaller circle to the right of it. You can make as many circles as you wish, but make sure you keep the Shift key held down. If you don't like a circle you've made, hold down the Option/Alt Key and deselect it with the Circle Selection Tool.
Once you’ve made your circles, fill them with white.
Now the fun part: Using the Eraser tool with a feathered brush set to an opacity of 100%, start to erase the middles of the white balls you've made. For this I adjust my brush size to about 75% of each ball and simply click inside each of them three times. That's all you'll need to erase to create your basic bubble. Just make sure you adjust your brush size for each bubble.
Now it's time to take your bubbles to the next level. Using the Paintbrush, set to feathered and 100% opacity, make short sweeping strokes on the upper left hand corners of each bubble. Be sure to adjust your brush size for each bubble.
Now it's time to make the background a little more interesting. With a large feathered Paintbrush make long vertical sweeping strokes with a darker blue. Here, you can stylize however you wish, just think hula dancers and mai tais.
Here I take a large feathered Dodge Tool set at 100% opacity and do small sweeps in light areas of the background just to add a little more depth.
I do the same with the feathered Burn Tool set at 100% opacity to the dark areas.
My last step is to take the Smudge Tool set at normal and 50% strength and blur some of the hard edges on my light reflections.
All done! This took about 5 minutes, but I could easily take more time and make it more elaborate. This is just the simplest way to make realistic looking bubbles. There are so many ways to do things in Photoshop. This method is one of the many I may use for a given project. You may have a better way. Always do what works best for you.
Here's an example of these bubbles in action: