Q: Please help!

So recently, my grandmother's husband passed away and had an iPhone 5s that my grandmother is now giving me. We factory reset it hoping it would basically make it a brand new phone. But, after selecting the language and country, the following message popped up:

"ACTIVATION LOCK. This iPhone is linked to an Apple ID. Enter the Apple ID and password that were used to set up this iPhone. (s*****@hotmail.com)"

And then at the bottom there is a hyperlink that says Activation Lock Help. Whenever I click that it reads:

"A password is required to activate this device because its owner has used Find My iPhone to link it to their Apple ID. If this is your device, enter the Apple ID and password you used to set up iCloud. If you were given this device or purchased it second-hand, you will need to contact the original owner to have them remove this device from their account. Additional information can be found at: support.apple.com/kb/TS4515"

What exactly does this mean? Will I ever be able to activate this iPhone? If I was to take it to a Apple Store, would they be able to open it for me? I have heard Apple is big on security compared to Android (which I have been using) and most likely will not do this due to privacy. Please help. Thanks!

Also, no clue what any of the communities to post to say as they are half blocked by my phone screen for some reason, so I selected a random one.