In general, if the "r" is placed in the end of the word or in the middle of a word, where the syllable is not the strongest (a sílaba atôna), it will be pronounced as the "r" in "door" /r/. For example: porta, Brasil. If the word has two "rr" its sound will be as in "hand" /h/. It's important to remember, though, that there are a lot of accents around the Portuguese speaking countries. In some places in Brazil people pronounce the "r" very strong as in "ruler", in some other places the "r" has a little vibration like in the sound a motorbike engine makes :) (it's hard to describe it) I hope I could help!

The letter "R" in Brazilian Portuguese has two main different sounds, This video looks very helpful to me: https://www.youtube.com/watch?v=1GqO_Cn9cjQ That a general accent, in some accents they replace the first 'r' in the video by the American English 'r', and in other accents they replace the first 'r' in the video by the long Spanish 'r'. "D" and "T" also vary depending on the accent, the only vowels that change how the consonants sound are 'i' and 'e'. 'di' and 'de' usually sound the same (somewhere between 'ji' and 'zhi' from pīnyīn). 'ti' and 'te' also usually sound the same (somewhere between 'qi' and 'chi' from pīnyīn).