The things on the right are nano dot things. Find them here. They work really well, but might damage your wall if you need to take them down.
Also, double stick foam tape like this, works really well, but takes the paint off when you try and take it down. Believe me.
Use a level to hang the clouds.
There’s also an iphone app called “measure” that has a level in it. But it seems a little dicey to me to hold the phone against the wall and your new, can-also-break-if-you-drop-it cloud.
Press the cloud where the dots are. If you do it between the dots, you risk snapping the cloud.
And you’re done! Enjoy your serene, peaceful clouds.