Do hostels provide everything that is necessary to stay during a couple of days ? What do you recommend to bring with me ? Should I expect they provide things like towels, soap or shampoo ? Do they have laundry, iron or ironing board ?
Hostels usually provide basic low cost accommodation and related additional services. The range of additional services is quite specific in each hostel. Guests have access to their bedroom, shared bathroom, common room or kitchen. Cheap hostels often provide bed linen, fridge, internet access and some games or maps for free. Other stuff like breakfast, drinks, locker, luggage storage, towels or hair dryers may be available for a fee. In some hostels these things can be provided for free.
I would say, that hostels provide everything that is necessary to stay for a few or more days. You should bring your personal hygiene stuff like tooth paste, soap, shampoo, towel etc. I recommend to bring a hanger for towel, tissues, flip flops and maybe an earplugs. If possible, you should come to a hostel with luggage, that can be locked. Some hostels may have a washing machine, iron and ironing board. When hostel doesn't have a washing machine, you can go to a nearest laundry.
In some hostels, there are available things like computer with internet access, vending machines, televisions, foosball, pool table and other entertaining games.