For starters, you should look the map for a commander if any is present. If so, he should be giving the orders (if he's a good commander and not just someone who wants to show his shining blue icon).
If no commander is present, people usually gather in "buses of player", in order to raid places with a massive force. It's usually a good group to learn WvW as well as doing things with lot of successes.
Eventually, you will want to do something on your own. If so, be sure to bring some friends along in your party. There are some thing a small group (or even a single person) can do:
- Raiding Supply Camps (be sure to avoid camps that has been taken within the last 5 minutes, as the Supervisor will have a strong buff)
- Raiding Towers with a ram (requires at least 4 person to be able to built it if untouched by the enemy)
- Scouting: intelligence is a need for every strategist. Being able to provide insight on the enemy progress will help the leaders to choose the right course of action.
- Raiding Keeps: there are times when a prolonged battle takes place between two (or even three) large forces on a map. And during these phases, a well organised group may be able to quietly gain control of a keep. Of course, you will need rams and thus enough supply. But I recall one time where I took Shadaran Hills with only 4 players of my guild. Of course, don't expect to succeed this unless you get some luck (We also were prepared to be wiped out before reaching the second door, but seems they were so occupied by the main battles that they did not take attention to us :P)
Don't feel oppressed by the player giving orders on the /map, you can contribute to it yourself. Don't hesitate to ask questions too, many players will be kind enough to help you.