This may just be the lightbulb. Check that the light bulb is properly screwed in and if there is no difference, then replace the bulb. Is it still flickering? This is an indication that there is a loose wire which should be handled as soon as possible. If you can, try to not use the light until the electrician arrives as loose wires can lead to fires and/or personal injury.
When looking at your electrical panel there should be one switch that is not aligned with the others. If you look closely it should show that it is in the off position. To turn the breaker back on you will need to push the breaker towards the off position first and then turn it back towards the on position. The breaker should click back into alignment with the rest of the others.
Standing for “ground fault circuit interrupter”, a GFCI is an extra safety measure to protect people from potential danger. GFCI are used in bathrooms, kitchens, unfinished basements and any place where the outlet may come in contact with water. The outlet has a mechanism that will turn off the circuit if it detects electricity going down the incorrect path, for example through water or a person.