If I delete pictures from my photos app, will they also be deleted from iCloud?

Depends on exactly what you have set up.

If you have the iCloud Photos option turned on in Settings ➜ Apps ➜ Photos ➜ iCloud Photos, then yes, deleting photos from the Photos app will also delete them from the iCloud Photo Library, but the photos would not be part of an iCloud Backup though. Only synced to the iCloud Photo Library.

If you don't have that option turned on, then no, it won't immediately delete the photos from the iCloud backup, but the next tine a backup is taken, it will not contain the deleted photos and will replace the backup that did contain them.

darele211 wrote: …if I delete a pictures on my photos apps, will it be deleted also in icloud backup account?

You could just try it! Take a picture, then go to iCloud.com and see the picture there. Then delete in on the phone, and see what happens at iCloud.

As Phil0124 says, it's a little confusing for us because iCloud Backup and iCloud Photos are completely different things. iCloud Photos refers to a section at iCloud.com where you can see the same pictures that are on your iPhone. iCloud Backup you only see on your phone at Settings>[name]>iCloud>iCloud Backup, and you can't see what's in it at all. Pictures from the Photos app can't be in both places.