How easy is it to fit a garage door opener?
If you're not comfortable with running electricity in a safe manner, then yes, you should have an electrician install an outlet in the ceiling near where you intend to install the opener.  You can run a split off the line that feeds the lights, but you do need to run the opener on an always-on circuit, so you have to know what you're doing there.

As for the installation itself, as long as you're reasonably handy, know how to find proper structural supports (ie: the framing), the installation should not be very difficult.  Obviously the install will vary based on the model but generally you'll install a mounting brace of some kind, which needs to be VERY securely attached to the structure of your garage (not just the drywall - but INTO the joists/studs).  The rest should be pretty simple as long as you read the directions carefully and plan it all out before you actually start.