With the A series, the first number is how 'good' it is, the second number is how new it is.
The 'goodness' number is from 0 to 5. 0 being the cheapest, 5 being the best.
Right now the a56 is probably the best budget phone from samsung. Above that is the s25fe and then the s25. The S series is the best samsung has to offer, though they are expensive.