The Hel penninsula is a sandy stretch about 50km long. The width ranges from a few km to a few 100m (on stormy days waves from the Baltic sea can break across the peninsula in some spots).
There are a few tens of windsurfing bases located at camping sites and in the local villages. The majority is concentrated in the western part of the peninsula, near its base. It is an extermely popular spot in Poland - during the season you will see hundreds of windsurfers and kite surfers on the water. One of the bases prides itself in being open all year round.
Most windsurfers and kitesurfers use the Puck Bay (south) side of the peninsula. You are sheltered by land from 3 sides and the winds, which are usually W or SW, will blow you towards the shore. Most importantly - the bay is shallow - you can surf many km from the shore and still be in chest or kneck deep water - so it is easy to get back riding by doing a beachstart. If your board does have a long fin you may need to walk a few hundred metres before you can get started, but this depends on the particular spot and the particular part of the beach. Great place for beginners and intermediates.
Wind is probably strongest in the spring and September, October. During the summer months it is varied, and unfortunately you can get stretches when it is 1-2B for many days in a row. It is best to have a fairly big freeride type board (130+ l) with an mid size (6m) and some big sales (>7m). But - expect to also have windy days where you'll be ok on a small board with a 4.5-5 m rig.
If you want to do some wave surfing you can walk accross the peninsula and try on the baltic sea side of the peninsula. Here you can usually expect a slightly offshore wind. Be warned there are no bases on this side - so you'll probably need to have your own kit and don't count on any rescue crews. There are also groynes every few hundred metres so it is quite challenging getting going on this side.
Staying there
Accomodation is very varied. For the best windsurfing go for one of the campings near the base of the peninsula. If your lucky you'll be able to find a pitch which is literally a few metres from the beach. Facilites at the campings are varied, some are quite basic, others are very good. Most have one or two windsurfing bases with storage, rental and training facilities. They also run shops where you can get your windsurfing and kitesurfing bits and pieces. If you do need to buy something there are also a few shops in Wladyslawowo - bigger, better choice & better prices then the ones at the campings.
Apart from that there are plenty of apartments and hotels of varying standard. If you are looking form something 'posh' you'll probably want to go for the village Jurata which is one of Poland's premier sea side resorts and boasts many nice (and expensive) hotels.