Open your Image in Photoshop, then i will remove its background
Then Open flowers you wish to use and remove background as well,After removing the background then drag them on top of your Imge
Go to Image - Image rotation to rotate flowers as you desire
Click on CTRL+T to resize and position flowers as you desire
Now merge all Layer
Make sure all layers are selected in Layer pallette then right click and select merge Layers
You will now have only one Layer
Now i will open an image that will be used as a background, then i will drag my image on top of it
Go to Image - Adjustments - Levels ( and adjust channels as you desire)
Go to Image - Adjustments - Brightness/contrast and set light as you desire
Below is my final Image
