Hash is just an extract from cannabis flowers, depending whether you're in the US or Europe hash will mean one of two different things.
In Europe hash is an import product usually from the Middle East, Morocco or India. It is made either by sifting off the kief (the crystals on the cannabis flowers which contain the THC) and pressing it into a block, or by rubbing the flowers in your hands until the crystals gradually collect into a squidgy ball.
In the US I believe hash usually refers to more refined cannabis extracts done using more advanced extraction methods and tends to be much higher in THC content than European hash (more of a true 'concentrate').
There is not much reason that the effects should necessarily differ between cannabis flowers and hash of either kind, although they inevitably will. The difference will be down to the strain the hash was made from, whether the process of making it may have omitted certain cannabinoids, and the strength of the hash.
For this reason it's quite hard to say what kind of hash is gonna have what effect, every batch will vary so you'll have to find out for yourself.
European hash tends to offer a more relaxing and mellow high than common indoor grown 'hydro' weed. This is because it is made abroad from large scale outdoor cropped cannabis which is probably a more traditional strain lower in THC and higher in CBD than our western highly selectively bred cannabis strains.
US hash I imagine will be different mainly because it will be very potent / high in THC even compared to professionally grown indoor hydroponic flowers. Additionally, the process of extraction may result in the loss of other cannabinoids or terpenoids and this may also affect the high.
Hash of either kind will almost always need to be smoked or vaporised to feel it's effects, if you want to eat it you will have to decarb it and cook it into food the same way you would with weed.
You don't wanna smoke mouldy weed, it could make you ill. Properly dried and cured weed should still look and smell nice and green and fresh but be dry inside and crumble up somewhat easily between the fingers, rather than squish up and get all sticky.
Good hash is probably a bit harder to spot, especially the European types, make sure it has a nice fresh smell and if it's a dry kind it should crumble well in the fingers back into fine crystals, or a squishy kind should be nice and malleable almost like putty.
Hope this helps
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