[how do i withdraw linden that i have earned to RL Account]

so i guess i dont understandthe whole selling my lindens thing how am i suppose to sell them and why is it i have to wait till someone buys them ? I guess i dont get why since other people have bought itmes from my with thier money why i have to go through a process just to get it converted back to USD when to put the money on it takes 30 sec.

[how do i withdraw linden that i have earned to RL Account]

I have been looking everywhere i  cant find out how and i am getting exhausted trying to figure it out.  I would like to withdraw my lindens to my RL Account to get the money i have earned through my store