18650 Cell boost converter to 4.8v (not 5v)
You say that your knowledge of electronics is very basic, so I shall not recommend a bespoke design.  It’s normal to use a constant-current driver for LEDs, not least because the current is very sensitive to the voltage applied.  If you can find a constant current driver that fits your requirements then you’re all good, although I think you may struggle because of the relatively low supply voltage.  As an alternative you might try using a resistor to limit the current:  you want to supply 1A to the LED and the resistor should drop (5.1 - 4.8) = 0.3V.  Using Ohm’s law, R=V/I so you’ll need a 0.3 ohm resistor with a power rating of at least 0.3W.  The nearest thing you’ll easily find is a 0.33 ohm part with 0.5W power rating.  If you place this in series with the LED you should be ok.  I note that 1A is a lot to ask from AA cells, so you may well be overdriving the LED which will shorten its life.  If you use a larger value resistor you’ll get slightly lower output but longer battery life, perhaps try 0.47 ohm.  As an aside, there are some good reasons why resistors have these oddball values - look up ‘preferred value resistor’ if you’d like to know more.