Page rank is an algorithm of google which google use to give a rank for websites starting from n/a to 10 according to their back links.
So if you need a good page rank for your website you must have good quality back links.
301 is a redirection which is used to solve 2 problems.
1) If we have 2 similar pages in our website and we don't want google read both of these we can use this redirection it is a permanent redirection.
2) If our website is opened with two url's such http.abc.com and https://www.abc.com
then this url is not google friendly so we need to redirect with our www url to www url so it can be opend only with www and if some one type only http then it redirect to www and always opened only with www.