@Marci1 Thanks for reaching out!
To clarify: are you asking about how to open the hydration bladder or how to access the panel on the pack that the bladder fits into? If you're asking about the hydration bladder, you need to slide the gray plastic piece off of the actual bladder, pulling towards the attachment loop. The bladder should be open and ready to fill! If you're asking about the panel in the backpack, the opening is on the upper part of the outside of the pack, right behind your shoulders. Typically there is a zipper pull, although sometimes companies will invert the zipper so it is upside down and lest prone to catching on something.
Hopefully this helps, please let us know if there are any other questions you have!
Hi @Marci1 . To piggyback on to what @REI-JohnJ said about the hydration bladder, after you remove the grey plastic slide, unfold the flap and then separate front and back flaps. I have found that when new, the plastic of these bladders tends to stick together; sometimes very strongly. To the point that it seems to be a permanent seal. After the first usage, or possibly 2 or 3, that issue goes away, but don't worry. This is a very watertight bladder.