There's an excellent free Ebook about opamps, it is called "Opamps for everyone" and you can download it here.
An Opamp is a device/circuit that tries to behave in a certain way, it amplifies the voltage difference between its inputs. Ideally an opamp would have an infinite gain and also work for every frequency and have no flaws at all. Obviously that's not possible so every opamp is a compromise.
The 741 was one of the first "usable" opamp ICs (a chip) and in its days (1970s to 1980s) it was very popular. We have moved on since then and have better technology to make better opamps. A limitation of the 741 is for example that it is useless at the low supply voltages we use today like 5 V. A 741 really needs a symmetric +/- 15 V supply.
I would not worry too much about what opamp is used as an example in teaching presentations. Usually the opamp is assumed to be "ideal" or at least good enough for the function that is explained.
The circuitry around the opamp, like a feedback network, stays the same whatever opamp you use. Focus on those circuits and how the opamp is used, not the model of the opamp as it doesn't matter much.
The internal circuit of an opamp is really only of interest to IC designers and experienced designers that can determine the limits of what the opamp can do depending on the circuit that is used. For example, I am an IC designer so I can look at the schematic of an opamp and see how close it can drive its output voltage to the supply rails from the architecture of the output stage (if that's an common emitter, common collector, common source etc...). However, in the specifications of the opamp there will also be information about this under "Output voltage range". So you don't need to know or look at the circuit, the information is also in a table. And that information is leading as it is guaranteed behavior. I could have missed something in the schematic or not understand it properly or the schematic could be incomplete (some manufacturers do that to protect their design).