The circuit is a hypothetical attempt at a constant current feed to the load. Once it is established that (on the face of it) the circuit has negative feedback you can move on and say that the inputs to the op-amp will always be the same (within millivolts).
Because Vin- has a fixed voltage on it determined by the pot all that remains to establish how the voltage on Vin+ is produced. This is simple - that voltage is determined wholly by the current through R3.
This means that you set the pot to produce a voltage on Vin- and the current through R3 adjusts to produce exactly the same voltage on Vin+. At this point equilibrium is reached.
The current through R3 is controlled by the voltage from the pot. What about the current through the load? Well, it's virtually the emitter current (R3 current) and so this circuit is an attempt to apply a constant current to the load.
Let's say the pot is set to be 9.5V - this means (theoretically, and on the face of it) that the voltage across R3 will be 0.5V i.e. 10V - 9.5V. This means that 0.5A flows through R3 and that current largely flows through the load. If the load is 10 ohm, the voltage on the load will be 5V. If the load dropped to 1 ohm, the voltage on the load would drop to 0.5V.
There are restrictions from the power supply of 10V. For instance, if the load were 20 ohms, the circuit power voltage hasn't got enough headroom to put 0.5A through the load and the circuit no longer behaves linearly.
What is wrong with this circuit - if you tried to build it, it would oscillate although the average current into the load may just about be kept at a fixed value. Why would it do this? It will do this because it has made the fatal error of not understanding the open-loop gain of most op-amps.
Most op-amps commercially available sail close to the wind in that with negative feedback they are close to becoming unstable - in fact some op-amps cannot work as a unity gain inverter. What makes this circuit worse - collector gain is potentially added within the feedback loop so now the op-amp has to cope with an extra bit of gain within the negative feedback loop and this, under most practical load conditions will make the circuit oscillate.
If the load is 1 ohm then most op-amps would just about cope with the collector gain being unity but the extra little bit of phase shift incurred makes it on the point of oscillation.
If the load is 2 ohms then the collector voltage gain is less than 1 and this circuit stands a chance of working provided that the load is purely resistive - any small amounts of capacitance will make this circuit sing because at high frequencies the capacitance will turn the collector gain greater than 1.
Forget about loads less than 1 ohm and don't really expect this to work in practise - there are better circuits for controlling load current.