If you are in terrain with high relief (think of the Swiss Alps), then you’ll have no trouble at all.
Consider how terrain features look when you are on them. (The Army, whence we stole these graphics, also teaches you to visualize the terrain features by looking at your fist and hand. An example of how that do that is in this presentation).
A hill is easiest, and its a very common feature. From the summit of a hill, the ground slopes down in all directions. On the map, it is the center of a ring or rings of contour lines.
A depression is opposite of a hill. It is fairly rare, but in a depression the ground slopes up in all directions. Such a feature is rare because nothing shapes terrain as inexorably as water, and water seeks an outlet. If it does not find one, in due course, it makes one. Depressions either are in very very arid climates, have some means of draining water direct down out of the bottom, or evolve into lakes or ponds. On the map, a depression looks like a hill — a circle — except that it has tickmarks on the low side, the inside of the circle.
In a saddle, the ground is higher in two directions that are approximately 180º from each other, and lower in the other two directions offset at 90º from the high ground. On the map, the saddle is where the lower contour lines on a hill merge to also wrap around the adjacent hill.
A more common feature puts you in a place where the ground is higher on three sides and lower on one. Depending on the dimensions this is a valley or a draw.
We think of the grounds at Hog Manor as “level,” but they aren’t, really, it’s more an illusion created by the previous proprietor’s landscapers. You actually have to go down a half-flight of stairs to get to the garage, but from the same point, up a full flight of stairs to get to the Music Room over the garage. The half-flight is absorbed by a high ceiling in the garage, preserving the illusion of a building with all its modules on the same level, until you start doing mental math. It’s architectural trompe l’oeil, and is so common most people never notice it.
In the front yard, this non-levelness manifests as two almost level areas with a retaining wall in between. In the backyard, a variety of stone features try to conceal the slope, but the ancient 18th or 19th Century stone wall between lawn and wood betrays the true slope of the terrain.
So the real understanding of “level” is — compared to what? We grew up on a less level lot, where careless riding mower operation could (and did) roll the mower. We had a similar experience, learning land navigation in the hills and mountains of New England, and then going to Fort Bragg where one must sink or swim in a navigation environment with much less relief.
In that case, you have to learn to look straight in the distance in the various directions around you, and be able to see where the ground is higher and lower compared to your standpoint — even if the height difference is only a hand’s breadth or two. Once you visualize where it’s higher or lower, you should see just that on your map. In time and with practice, the correlation between map and ground gets to be second nature, and is only disrupted if you are in a new location with very different relief. Even then, the more experience you have, the more easily you orient in new physical environments.