Hi Keren,
The general assumption is that a cathedral is just a large church. However, this is not actually the case. There is a very specific criteria that a church must meet in order to be considered to qualify as being a cathedral.
The difference between a church and a cathedral is simply that a cathedral is a church that also serves as the seat of the bishop. Normally it is the main church of the dioceses. In most cases the cathedral will be the largest and most impressive church in the dioceses.
Kind regards,
Georg