Allah ki marzi and duaa....confused

Salam.
i am vry much confused on two things...can anyone here help me in dem..

1) wat is Allah's will?? Allah ki marzi? if evrythng dat is to happen or happens is by Allah's will....y do we pray?? why do we ask Him for any certain thing. jab Allah ki marzi se hi hona hay sab, Allah ki raza se, tou hu duaa kyo mangatay hain?


2) plz EXPLAIN the following lines...wat do they mean? detail may koi samjha sakta hay?

Ay ibnay Adam ek teri chahat hai aur ek MERI chahat hai.
Hoga wohi jo MERI chahat hai pas agar tou nay supurd kardiya apnay aapko uskay jo MERI chahat hai.
Tou MEIN tujhay who bhi donga jo teri chahat hai.
Agar tounay mukhalfat ki uski jo MERI chahat hai
Tou MEIN thaka donga thujko usmein jo teri chahat hai.
"Phir hoga wohi jo MERI chahat hai."