I can relate to your frustration. When I first purchased my first GPS, Garmin GPSmap 478 (a simple auto-boat unit), I was totally confused. I found the manual very frustrating and could not figure out why it would show auto and not marine charts. I played with my unit for about two days before I got the hang of how to do anything with it. I almost returned the unit..
To put this in perspective, I do not consider myself a tech-idiot. I have taught courses in computer hardware, software, and storage networking at various points in my career. I'm no tech-genius either. My kids will vouch for that
I now believe that if someone with some experience with this unit could have shown me the basics, I would have saved a lot of frustration, and probably 12 hours.
I suggest that you go to the nearest West Marine, or other store that carries this unit. Start playing around with it. Sooner or later a sales person, or another customer will come by to see what you're doing. Strike up a conversation (If you meet a sales person, I suggest that you do not disclose that you have already bought the unit. The conversation will get real short
There is a TON of experience here in SailNet. However, your question
Can anybody tell me how to operate a Garmon 540 GPS for my sailboat?
is far too vague for us to offer specific useful information. This is why suggestions like "connect it to power," "turn it on," "mount the antenna," "look at the screen," and "RTFM"
will be offered to you.
Alternatively, if you'd like to pay my expenses, send me a PM and I will come to your boat and show you the basics... I hope that you have a nice boat, because it could take me a while to figure it out. I guarantee that I will have a full report by September