How to train a CAT to pee??

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I was wondering about this question how to train a cat to pee/bowels in proper place or to pee outside??Like dogs,they are clever enough to follow what we train them... And they always scratch the doors when the door closed and if they wana go for a pee,so we know that he/she wana go outside.But how bout cats?I think cats have less brain(ability to follow our instruction)than dogs. How you train your cat to pee at proper place?? Isn't it disgusting and nasty to see them pour everything in your house?Will your cat make such a mess?pee inside your house,your bed?