High grade is sorta mid-difficulty when it comes to gunpla. Usually about as big as the palm of your hand, have decent articulation, and are fairly detailed. But a lot of times color accuracy isn't... The best. But high grade is still good for beginners.
Master grade is a bit more complicated, unlike high grade which is 1/144th scale, which is palm sized, master grade is 1/100th scale. Meaning it's usually about double the size of a high grade.
These things aren't the MOST detailed, but still have more detail than high grade, and are usually more durable, have better articulation, and way more cool mechanisms in the joints. A beginner could build one of these, but I recommend building a few high grades first before you try a master grade.
Next is real grade. These things can be an absolute pain to build. They are 1/144th scale, but have far more detail and mechanisms than a master grade, and are often referred to as small master grades. These have VERY small parts, but almost always turn out BEAUTIFUL
The final difficulty is one I haven't even experienced. Perfect grade. Since I have been building gunpla for a few years, I think I could build one. But it would definitely take DAYS.
(Note that most of these are guesses)
It has more detail than real grade, probably more size than master grade, and more articulation than you could ever need. Perfect grade kits are gods among gunpla.
There's also one more grade but... This one doesn't really count. It's called entry grade, same size as a high grade but far less detail and likely far less articulation. I've only built one entry grade and I did it in just over half an hour.
