There are a number of different ways you can record the tracklog. If you are in a vehicle, plane, boat or whatever, you can put the device in a dash mount and plug in a power adaptor. But for handheld use, you need to consider battery life, and the possibility of unintentional screen touches.
Memory-Map has the ability to use the GPS and record a tracklog while the app is in the background, or even with the screen turned off. You can enable this option in the Settings > GPS Settings dialog. Be careful, because, if you forget to turn off the track Logging when you are not using your device, it will have a flat battery next time you need to use it.
Alternatively, if you have the device mounted on the handlebars of a bike, it is useful to have the screen automatically dim after a minute or so, but be able to turn it on with a quick tap on the screen. To do this, go to Settings > General Settings, and turn on "Disable Screen Timeout". Note: this feature is platform dependent. Some devices to not allow apps to keep the screen on.
Sharing and Importing GPX data