In some hostels you find lockers and other not. Some offer saves for your most important things like money, passport, photocamera and so on ...
But in most of the hostels, you just put your backpack under your bed, take your important things with you in town or when you sleep with you in your sleeping-back and that's it ... not always safe...
Have a look here:
Select the country and city you want to stay, then accommodation:
There you find hostels and in the descriptions of most of them you will see, if they have lockers or not ...!!
And do not forget: travellers are mostly very very nice people, but there are also a lot who run out of money... and you can understand what this mean!
Book your hostel here: rail.shop/hostelworld