We have many 'rules', and also many exceptions. Unfortunately, unlike Spanish, there is not a one-to-one relationship between sound and spelling. And as you've probably realised, English also has more vowel sounds and diphthongs (combined sounds) than Spanish does. As for the book/floor question - this is an issue about the letter 'r', which lengthens and completely changes the sound of the letter before it. Book rhymes with 'cook' and 'look', and has the same vowel sound as 'put'. 'Floor' (in British RP) is an elongated 'or' sound, similar to 'for' and 'more'. The more you listen to natural English, the more you'll get a feel for the sounds. Another useful thing for you to do is maybe watch English TV or films together with English subtitles, so that you experience the look and the sounds of words at the same time. And if you are ever not sure about a pronunciation, many online dictionaries include sound files, with examples of both American and British pronunciations of words. I hope this helps.