Draw equal rectangles, 1 to 10 cicle.

for(i=1; i <= 10; i++) {
    instructions
}

Effect: repeat 10 times the instructions

i     variable of the cicle. Every cicle
      it increments by 1, as effect of i++
for   is a cicle with variable
<=    less or equal. 
Attention !
=<    syntax error !!!
<=    correct

Cicle will continue until i <= 10

Numbering from 0

for(i=0; i < 10; i++) {
    instructions
}

Infinite cicle

for( ; ; ) {
    instructions
}