There are lots of places to go drinking in à lesund. However, the price level is quite high, expect to pay 80-90 NOK for a pint of beer. This price level has resulted in a youth culture where people gather at someone's home first to drink and usually don't go out before midnight.
Most establishments are open, but the more youth oriented ones are usually close to empty before midnight. If you're a visitor out for some youthful partying, it might therefore be advisable to go somewhere else for a few pints first and then go out looking for where the action is after midnight.
All establishments close at 3 am by Norwegian law. This usually leads to complete chaos as most people stay until then and people standing around for hours in taxi queues. If you need transportation, it is therefore advisable to call the taxi company no later than 2 am. If you live in the city centre, it might be advisable to plan on leaving a little earlier as well, just to avoid drunk people in the streets.
If you want to buy alcohol from a shop, beer can be gotten in normal supermarkets until 8pm 6pm Saturdays for 25 NOK for a 1/2 litre can. Anything stronger than 4.7% can only be got from state authorised Vinmonopolet until 6pm weekdays, 3pm Saturdays, located in Kremmergaarden in the centre, as well as the Moa shopping centre in the suburbs. Note that supermarkets are not allowed to sell any alcohol after these hours, even if they are still open. Also, alcohol is not allowed to be sold in shops during Christian holidays such as Easter or Christmas.