Hi. When I had a chihuahua he was pretty good about going to the bathroom. At first he made some mistakes in the house (the mistakes are so tiny because they are so tiny), but I took him out every couple of hours. If he looked like he was about to go, I would quickly take him outside. Taking him out often, and then praising him after he went, seemed to work pretty well. Chihuahuas are very loyal to their masters and will actually choose one person to attach to, in most cases. They want to please you.
I did try one of those pads you keep in the house, my dog did not want to use it. They are small, so if your puppy will not use the wee wee pad, you are going to have to take them out often because their bladders are not that big.
Some people crate train. I personally do not use crates, but I heard that works well also.