If no fields are listed, call the stores and ask. It usually provides a store and field directory in the back of every issue. Call the field and get directions, hours and prices. Find out what gear they supply, and what you'll need to bring. Arrive at the field early and prepared.
Most fields charge a flat rate for a full day of playing.
If you're going to walk on to a field, it's generally more fun if you go with some friends. If you have a paintball team, you can all go to the field and play together as a team. Sometimes the field will let you play as a team against all the walk-ons. Talk to the field director. At any paintball field, you must have a barrel plug for your gun to prevent any accidental firings.