An 'environment' is just a magnetically, and so chemically, different part of a molecule
An environment is dependent on its surroundings, and so different surroundings give rise to different environments... As a rule of thumb, each new carbon atom or proton is a new environment, on the condition that symmetry isn't exhibited (more later)
'Surroundings' in this case is which carbons and protons are adjacent to particular protons or carbon atom...
Hence, if two parts of a molecule have the same 'surroundings' i.e. they both have the same groups adjacent to them, they're said to be of the same environment as they're chemically equivalent... This particularly arises when a molecule exhibits symmetry
For example, in both proton and carbon NMR, methane has one environment: there's just one carbon atom (hence one carbon NMR environment) and the four hydrogen atoms are adjacent to one equivalent carbon atom (hence one proton NMR environment)
The same can be said about ethane: this is a symmetrical molecule, so one CH3 group is adjacent to an equivalent CH3 group... Hence, only one environment is observed overall for both NMR methods
However, what about something like ethanol? This isn't symmetrical anymore, unlike ethane, as there's an OH group involved...
For carbon NMR, two environments will be observed: the CH3 group is adjacent to a CH2 group (hence a first carbon NMR environment), and the CH2 group is adjacent to both a CH3 group and an OH group (hence a second carbon NMR environment)
For proton NMR, three environments will be observed: the three CH3 protons are adjacent to two CH2 protons (hence a first proton NMR environment), the two CH2 protons are adjacent to three CH3 protons and an OH group (hence a second proton NMR environment) and the OH proton is just its own environment (hence a third proton NMR environment)
For practice you can search the NMR spectra for simple alkanes, predict what how many environments they may have, then have a look at the spectra
It all takes practice, and the problem with NMR is that at first it is difficult to understand because it's a very applied field of Chemistry...
However, after some practice (it won't take much!) you'll start to be able to look at molecules and read off their environments very easily