Ranger 690, That GPS is quite possably one of the best tools in modern Man's inventory.
Take the time to learn the basic functions such as "current location""mark location" "go-to points" and track logs. Pay particular attention to the set-up page...you gotta know how to change the settings for it to work with different maps.
Now that you have it, you are open to a whole new world of exploration.
But it's not the "silver bullet" that you think it might be. It can only let you know about places that you have "been". True enough, it can get you back to where you started, but that is only the very tippy top of the iceburg of possabilities.
Learn about topographical maps, grids, grid coordinates and orienting.
I know of a GREAT BOOK that lays it all out...I should know...I wrote it.
But even if you go another route, learn about reading topography and finding maps to use in your location, and how to accurately use them...Thats what makes a GPS such a wonderfull tool.