Resolved questions
sentences by: أقبل على and من قبل

من قبل = before
أقبل على = it have several meaning it could mean to embark upon, undertake, enter upon, proceed to, engage in
- to devote oneself to, dedicate oneself to, apply oneself to, turn to, attend to, give one's attention to, occupy oneself with
- to take an interest in, be interested in , to pounce upon or at, rush upon
or it could mean about as what kumail mention above

i will give examples for them ..

first of all من قبل which mean before
example
لقد رأيت هذا الشخص من قبل = i'v seen that person before ( lagad ra'ayt hatha alshakus min kabil )
لقد أتخذت قراري من قبل ولن اتراجع عنه = I've made ​​my decision before and i will not retract it ( lagad itakhdtu karari min gabal wa lan atarakao anh )




about the next one

أقبل على first meaning like what kumail said about

احمد اقبل على الموت Ahmed is about to die ( ahmad akbal ala almaot )

turn to

فأقبل على الناس = and he turn to people ( fa agbal ala alnas )
ثم أقبل علينا بوجهه 'then he turned his face towards us ( thumma akbal alyna bi wajheh)

أقبل على العمل = means he attend to work , stuck with it , which mean he makes an efforts in his work ( agbal ala al'aml )
أقبل على الدرس بجد و نشاط = he come or he attentd to the lesson , he makes an effort on it (persist in effort to do sth) ... ( agbal ala aldars be jid wa nashat )

sorry i cant find in english the exact word or translation for it


but hope it useful .. good luck = )