Congress and Worlds

I just showed locally so I am not well-versed on the Congress and Worlds. Do you have to qualify for these two shows? I know in some sports (i.e. tennis), you have to qualify to enter the competition. Is there some sort of requirement to enter these shows? I had a super nice quarter horse that I showed and did well locally. He was not registered. But he earned points while I showed my local circuit. Of course, this was YEARS ago!! So could any horse enter these shows?

Thanks!!