This is such a great question, I'm so thankful you asked it Shawan!
The mind learns most easily when it can group things together. Too much data (as you mentioned from trying to learn them all at once) becomes overwhelming.
For learning ranges, I like the following approach (and I highly recommend using the preflop charts tool at Pokercoaching to help
https://pokercoaching.com/preflopcharts/)
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Start with 4 key ranges
#1 The Button (this is your widest range, and if you get it down the others become easier)
#2 The Cutoff (second widest range at around 25%)
#3 Middle Position (say a 15% range)
#4 Early Position (a 10% range)
For each one, notice what the worst hand of each type you open
-What's the worst pair you open from that position?
-What's the worst suited ace you open?
-What's the worst offsuit ace?
-What's the worst suited connector?
-What's the worst offsuit connector?
-And if you want to go deeper: worst suited king, queen, jack, etc.
-And deeper: worst suited 2 gapper, 3 gappers etc.
This way you only really have to remember about 5-7 hands per position, because you'll know that any hand STRONGER than the WHEP (worst hand ever play) is an open!
Next I would look at big blind defending range
For this do a similar exercise to previous, and examine
#1 BB defending range vs button
#2 BB defending range vs cutoff
#3 BB defending range vs MP
#4 BB defending range vs EP
#5 BB defending range vs SB (small blind)
Now, these will be your baseline. When faced with smaller raises, you can defend more hands that the charts say. When faced with bigger raises, you'll want to defend fewer hands than the charts say.
Vs a weaker opponent you can get away with playing a few more hands, vs a really tough opponent you might choose to fold the worst hands on the chart.
It's important to realize that with these charts, the hands at the bottom are profitable (but just barely) if you play really well after the flop. When you are starting out it's often wiser to play tighter than the charts suggest, so as to avoid sticky situations.
Finally as you mentioned 3-betting ranges are worth looking into
There are 2 types of this range, linear and polarized
For the linear range, you just need to know the top 10%, 15% of hands (which you'll already have learned from the opening ranges study)
For polarized ranges you'll want to know the categories of hands
#1 Value hands (can get called by worse hands)
#2 Suited Aces + Faces Bluffs (great semi bluffs and contain the ace or king blocker)
#3 Offsuit blocker bluffs (will consist of hands like AJ, AT, KQ, KJ)
#4 Board coverage bluffs (suited connectors and gappers like 97s, 85s, 54s, etc.)
If you use the tool to study, it will give you specific ranges to use based on the position of the opener, your position, stack size etc. And all this is near impossible to memorize...
So what's more important is to UNDERSTAND the principles behind why you may want to add certain hands to a range, vs not play them.
This will depend on your opponent, how wide they open, how much they fold to 3-bet, when they defend vs a 3-bet whether they do it primarily by calling or 4-betting, how well they play postflop, how deep stacks are etc.
To keep it simple when starting out
Vs a raise, try to only play hands equal or stronger than the hands your opponent opens
When 3-betting, just use your strongest hands, and as you get more confident in your place start adding in those category 2 and 3 bluffs mentioned above.
For opening, mark down any hands you are unsure of when you are playing and then check afterwards if they are on the chart or not. The more you practice it, the more it will become second nature to know what the 'bottom of the range' is. And once you know that you'll be fine.
Don't worry about getting it perfect right away, just focus on trying your best and being excited to get a little closer to optimal, a little more refined each session and within a month you'll probably have the ranges down pat!
Hope that helps
