Sevan is a city in Lake Sevan Region. Though it is near the lake, it is not a lakeside beach town. Accommodation options are much more plentiful by the shore. The city is, however, quite close to the most popular beach areas, and is a helpful place to go shopping, visit a doctor, and source of other products and services that towns can provide.
Vans (marshutni) depart from Yerevan to Sevan a few times a day. You can get relatively close to the town by taking transportation heading for Vardenis, Dilijan, Ijevan or Noyemberian and getting off part way, but getting to town might be a little complicated with the latter three. Taxis from Yerevan or anywhere else are another option, at 100 drams (.33 US$/km).
Walking around the city is easy by foot. Taxis are plentiful if necessary.
The area has swimming of course, but there is also wind surfing on the lake, and some sail, paddle and row boats. Hiking and camping opportunities are endless as well.
If you live in Yerevan, and are in this area, you can buy fresh fish, crawdads, marinated fish patties that you can take home to barbecue/fry immediately or freeze, and smoked fish.
Fish! And of course crayfish/crawdads. These are the main products of the region, and whether you eat the fish barbecued, fried or smoked, it will be delicious. The crawdads with a beer are excellent as well. The Harsnaqar hotel complex near town has some unbelievably good crawdad kebabs, which aren't cheap, but might be worth splurging on.
There are some fast food place in town, and cafes, but most of the good places to eat are on the shores of the lake, a bit north.
There are no special places to drink here aside from a few cafes, but wherever food is served, alcohol is available. Most places have a limited selection of vodkas, cognac, wine and beer.
Although there are some hotel options in the city, your best bet is to find accommodations at one of the lakeside hotels, camp, or stay in Yerevan.
Getting out options are the same as those getting in. Vans, buses and taxis.