Photos app and iCloud I have my photos saved in my 'Photos' application on my Macbook Air. I also have them saved on my iCloud (i can see them what i log on icloud.com). Now, if i delete photos from my 'Photos' application, then will they be deleted off my iCloud?

I only have a small amount of storage on my MacBook Air and so far they're taking up too much space.
Yes, it will delete them from iCloud.
If you need more space on your computer, you should get an external drive and move the photos onto there, then delete them from your Mac.