This root has no working verb, just one powerful concrete noun, rosh, the head, and everything that radiates from it. The head is the top of the body, so it becomes the chief, the leader, the top of any list. And what is at the head of time? The beginning. From there grow the word for 'first', the word for 'beginning', and בְּרֵאשִׁית, the first word of the Torah, 'In the beginning'. One head, and a whole map of leadership and origins. Every word is verified against pealim, niqqud included.
There is no everyday verb on this root: ר־א־שׁ lives entirely in its nouns. That is unusual but normal, some of Hebrew's oldest concrete words (head, hand, house) anchor a family without a verb behind them. The meaning is carried by the mishkalim instead.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.