This is estimated value of your monthly earnings based on the processing power of your PC and current BTC exchange rate. This value may fluctuate in the course of a day, this is perfectly normal. When your computer is busy - the value slightly goes down, when you do not use your PC - it goes up.
Pending value is the value of your earnings which will be paid to you. All the money you earn with the app will be added to your Shorte.st account, and you will get them on payment day (10th day of each month). Withdrawal options available are: PayPal: minimum $5, Payoneer: $20, WebMoney: $5.