What goes in a resignation letter? Is resigning the right choice?

How do I resign? I've seen a lot of people post about resignation letters. What are you supposed to write in them? What's the point?
More interesting (to me) is the question SHOULD I resign? If not, what should I do instead?
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[@AzKat69]

Simple version, which applies to everyone (and no, companies do not "dictate" how you have to resign).
"Hello, this email is to inform you that I will no longer work at this company.
Today is , my last working day is .
Thank you for your understanding, it was a pleasure knowing and working with you."
Sent to: your direct manager
bcc: your personal email to get yourself a copy, regardless of company policy (manager won't see that, but it will be visible in the original email headers if someone with slight training looks into it).
Simple like that.
Leaving "any" job should be done with as little friction as possible.

[@jaredheymann]

Very helpful information, as always! So few people know what to expect when quitting a corporate job for the first time. Many people don't realize the potential that leaving to a competitor leads to an immediate walk-out. As you say, it's a silly policy, but I don't think most individuals understand this is a rule until they see it.
Good advice to go to your manager and share that you're "considering" another offer to understand how your company responds. Even if you're not open to staying, its a learning experience to see the whole conversation and how your current manager and company react. It's a missed opportunity on many fronts to just quit.

[@ianmccullough7294]

"...you understand all these things that no one else understands" == Bazel, amirite!??!

[@howigothired]

All Bazel all the time, haha.