Well, your question will require a lot of information that is already out there. So, I suggest you do some study and come back, if you have specific questions about certain operations. I often post broad questions, because I do not know where to begin, nor what terms to search. Here is what I think will help you...
1) This is a rather typical constant current source circuit.
2) The heart of the circuit is the operational amplifier.
3) The op amp is fitted with a feedback loop circuit
4) The feedback circuit gives the op amp the "information" needed to adjust the current, to keep it at a consistent level.
I suggest that you look on YouTube, for these tutorials
1) Op Amp operations.
2) Feedback loop circuit operations - both current and voltage.
3) Precision current source circuit.
You probably won't have to spend more than 15 minutes, per subject.
There are special all-in-one ICs, just for this purpose. Check into those, at your favorite supplier. I like Mouser.com.
Do well and we look forward to your future questions.