I have a corn in my foot and it its very painful, I can not walk :(

you need to get it cut out professionally by a chiropodist or foot health practitioner...

Defiantly go to the chropodist they will hopefully sort this for you, try not to attempt to do it yourself you will make it worse

Please do not use the over the counter plasters.
They contain salicylic acid and will kill the healthy tissue.
Do u have any medical conditions?