To be a delegate (get to vote on resolutions and officers) you must be a paid-up member of the Democratic Party by a certain date later in May (can't find the exact date just now but it must be coming up soon) and contact the chair of your county party to be appointed a delegate. If that doesn't work out, you can still come as a guest and register as late as the day of the convention.
Register for convention online: http://www.wisdems.org/events/convention
Join the party online: https://wisdems.zissousecure.com/membership
Find county chair: http://www.wisdems.org/about/county_parties
The first night of the convention, Friday, we mostly hear speeches by elected representatives and others, and afterward there are "hospitality suites" where those attending are offered refreshments. DUers have historically gathered to chat then too. On Saturday there is debate and voting on the platform and resolutions, voting on state officers, and probably more speeches. Another nice feature are the booths set up by many progressive organizations and vendors where you can find out about their work and pick up literature throughout the convention