Can I give out my e-mail address here, or are users not supposed to do that?
You are welcome to put your email in your profile, but please don't spam the Q & A site.
As everyone else has said, you can post your email if you want, but its a good idea to take precautions.
However, if you're asking if you can post your email and request users to email you directly rather than go through the answer system, then no. Your email address will be removed and you'll likely get comments about how bypassing the Q&A system defeats the purpose of the website. Answers should be posted on the site for the benefit of everyone, private help is usually discouraged.
It's never safe to publish your email address on an open web site. If you want someone to get in touch set up a new temporary address and use that until you're sure you can trust them. Even if the people on the site are trustworthy there are people out there harvesting every publicly available email address and selling them to the spammers and mass marketers.
If you really want to give out your e-mail you can either in a question, answer or better still in your profile.
However, it will be publicly visible and readable by spiders etc. so you might want to make it harder (but not impossible) to work out what it is.
You can if you want to. You should probably keep yourself safe and try to obfuscate it in some way. Use something like myusername [at] whatever dot com instead of just saying firstname.lastname@example.org. It will at least keep the dumbest email scraping bots away.