please explain these string methods in java and provide examples

char charAt $($int index$)$

int indexOf $($char ch$)$

int indexOf $($char ch$,$ int pos$)$

int indexOf $($String str$)$

int ndexOf $($String str$,$ int pos$)$

String concat $($String str$)$

String replace $($char charToBeReplaced, char charReplacedWith$)$

String substring $($int beginIndex$)$

String substring $($int beginIndex, int endIndex$)$

String toLowerCase$()$

String toUppercase$()$