The beach closest to the town of Skiathos is called Megali Ammos. It is relatively narrow as a beach and long and combines sand with small pebbles. But to get there, you have to go down a steep hill.
The sea is quite shallow and is the most used beach on the island. There are plenty of sun loungers and umbrellas to accommodate many tourists, while being well protected by the north winds.
In Megali Ammos you can find bars and tavernas up to the shops to do your shopping, and of course there are plenty of hotels and accommodation.