You interacted with him at the store, correct? So he knows you, at least a little bit...Right now it's the car ride home, the new cage, the new room, etc. It does sound like he's hissing a little bit, so like Itzjbean said, just sit next to the cage and talk to him, maybe offer him a treat like a millet spray through the cage bars, etc. Just let him settle-in and realize that his new surroundings are safe. As already mentioned, it just depends on the individual bird how they are going to react, I handled my Cockatiel from the minute I put her in my truck to drive home, she sat on my shoulder for the 90 minute drive! But some birds just get very spooked...Sometimes I think that letting them alone in a totally new cage, new house/environment, etc. like everyone says you should is actually much worse for them, especially for a hand-raised baby who is used to having people around all the time and to take care of them, and then suddenly BAM! they're in a new cage in a new house and left totally alone...I would think that would freak them out much more in that particular situation...So just sit by his cage and talk to him, maybe put his cage in a room with a TV or stereo so he can get used to the noise, that can often settle them too, just seeing you doing your normal thing around him...