You can look for interesting communities at dw_community_promo.

You can look for people or communities which share your inerests by searching other people's interests.

If you want to read random people's journal entries, to see if they say anything interesting, you might want to check out the members' page for this comm or the members' page for the community promo comm, which will pull up a cross-section of DW users.

If you are wanting to know how to use the service on a technical level, the FAQ is pretty comprehensive.