How you record waypoints and tracks depends on the receiver, so study the manual, and practice a little before launching your first mapping project. When first turned on, a GPS receiver starts listening for satellite signals. Your receiver needs a 30-second message from each satellite to use it for navigation. During this time, the signal strength bar is hollow, and the satellite is not usable. Your receiver may remember a locked satellite for several hours, even while turned off, making acquisition quicker the next time.
More satellites means less error.
For an accurate GPS location, wait for a lock on most or all of the available satellites. Always try to maximize your coverage, even beyond the four satellites needed for navigation. Even with a good view of the sky, acquisition can sometimes be difficult and slow. GPS signals shift frequency a lot - predictably, in a programmed sequence, and unpredictably, from speed and temperature variations. Searching for all 24 satellites could take 10 minutes or more.