I am new to Japanese and started learning only like 3 days ago , I was told I should start with the radicals (human,legs,ten,etc.) but how should I start to actually learn how to pronounce and read the japanese letters?
My personal opinion is that you should learn the proper pronunciation at the very beginning. Like it or not, when you start to learn to read, your brain will make its own interpretations of the sound, and every time you read a character, it will reinforce that possibly wrong interpretation. The longer you wait to learn the pronunciation, the harder it will be to unlearn the wrong interpretations your brain made and reprogram it with the new ones(aka you will have a strong foreigner accent).
Listening to a lot of helpful audio and having a Japanese friend to practice can be tremendously helpful.