I have a picture in my textbook that is confusing me as to how they are different.I tried looking for some info on the internet, but could'nt get it clear.Please help me.
I will try to help. But, in the future, please post a picture of the confusing diagram to help us help you.
edit: now that I see your diagram, I'm not sure if this answer is helpful. Will re-consider and possibly edit this response. Thanks for including it!
Grana lamellae refer to the lamellae (membranes) in direct contact with photosynthetic stacks (grana), where the stroma lamellae are the ones that are connecting between individual stacks (see here). My understanding is that they are functionally and compositionally very similar, the only difference being the region of the lamellae in question (link to paper, sorry for JSTOR paywall). Check out the Wikipedia page for Chloroplasts for some more diagrams. Maybe one here will help this make more sense to you!