If your camera has a sensor cleaning mode, trying that would be the first step.
If your camera is mirrorless (i.e. remove the lens and you see the sensor) using a blower brush to dislodge the dust would be a good thing to try. Don't touch the sensor, and if you hold the camera with the opening pointing down the dust may well leave the camera for the outside world.
If your camera has a mirror, you're going to have to consult the manual to get it locked up out of the way to let you gain access to the sensor.
Follow the instructions in your cameras manual for how to lift the mirror and then blow dust off the sensor with the camera held upside down. Refit your lens.
If the sensor is really dirty then it may need a wet clean, but don't worry about that yet - just use the spot healing tool in whatever image processing package you use to clean up the dust spots until you've tried the rocket blower.
As others have said, you might seriously be better off putting the money into a second hand DSLR. Something like a 1000D from canon is about £70 from MPB, and an 18-50 kit lens around £35.
It really does depend on your budget and the repair costs.
You *might* be able to re-coup some of the money selling the a3400 on evilbay as "Spares or repair", but you absolutely need to show the extent of the dust bunnies if you do, so that they can't claim anything back off you.
not necessarily he might be using digital zoom.
Things inside the lens would not be in focus and would not look like that. if the rear element is very close to the sensor it might be on that.
In any event this is a compact so will need a major strip to fix. If it is still in guarantee you could have it done for free. other wise it looks like a bin job.
Time to buy a new camera. If you want the same then Amazon have them used, from private sellers, for around £60, which is likely what you would have to pay to have it cleaned but I'd look for something a bit more up to date and from somebody like Park or Camera World where you get 6 months guarantee.