Arachnophobia can be a hugely negative force in your life, but that does not mean that you are alone, nor does it mean that you are unable to deal with it.
This is for people who experience such crippling fear and anxiety at the sight of a spider that they would legitimately prefer to burn a house down than go back in knowing there was a spider present. Your phobia may be extreme, but that's ok, because there is always a solution.
The first thing to do is understand about spiders makes you upset. This is going to be best done by you researching spiders a bit, whether you choose to do this through books or the internet is up to you but the internet with videos and image-based learning methods is really helpful, as it means you simultaneously learn and look at spiders.
Even if you can only handle it for spurts of time at first, that's alright, as long as you start trying to build up that time spent looking at spiders.
This step may take some time, but persistence is crucial. Take your time, while slightly push yourself.
If you'd prefer, there are alternative ways of doing this as well. An example would be finding newspaper articles with pictures of spiders and cutting them out, so you can get used to the idea of seeing spiders.
Once you have spent this time thinking about and researching spiders, try and make a few notes of what it is that seems to scare you the most about them. This can be as silly or as serious as it needs to be, even if it's just 'everything' about them that upsets you.