Internal Folder not Writable


I am trying to get my YouTube PHP based setup going but I keep running into chmod issues.

I have myself zero experience with chmod and after several tries I still haven´t been able to solve the problem.

Would be awesome if someone can help me solve my problem on those 2 lines:
Thumbs cache folder (/home/ubuntu/workspace/storage/cache/thumbs) is not writeable
Media thumbs storage folder (/home/ubuntu/workspace/storage/media/thumbs) is not writeable