为 (wèi, 4th tone) is the preposition 'for / because of'. The same character read 为 (wéi, 2nd tone) is the verb 'to be / act as / become'. Reliable trigger: if 为 introduces a beneficiary, cause, or purpose (为了, 因为, 为什么, 为人民), use 4th-tone wèi. If it links a subject to a role or outcome (成为, 认为), use 2nd-tone wéi.
grammar
为 often introduces a beneficiary phrase before the main verb: 他为我做饭 (he cooks for me). The longer form 为了 marks a purpose clause that usually leads the sentence: 为了学中文，我去了中国 (in order to learn Chinese, I went to China).
Components
ideograph
为wèi
for; because of
Same modern shape as the wéi reading - a cursive contraction of traditional 為 from the 1956 simplification. The wèi reading is functional rather than visual: when the character takes a preposition role ('for', 'because of') it shifts to 4th tone. No part of the simplified silhouette signals the tone change; learners rely on grammatical context. Indexed under Kangxi #3 丶 (the dot radical) by tradition; the radical isn't visibly meaningful in the modern form.
Filed under radical 丶 (diǎn, #3) by convention. 丶 is not a separate component in 为, so no strokes are highlighted.
