A force curve answers one question: how hard does the switch push back at each point of its travel? The horizontal axis is how far the key has gone down, in millimetres. The vertical axis is the force needed to hold it there, in gram-force (gf).
Four things to look for
Starting force. Where the line begins once the spring is preloaded. A high start means fingers can rest on the keys without pressing them.
The bump. On tactile and clicky switches, a rise and fall near the top. Its height above the line is what you feel; its width decides whether it feels like a crisp step or a soft hill.
Actuation point. The marked dot: where the switch registers a keypress. On most MX-style switches it sits around 2 mm.
Bottom-out wall. The near-vertical climb at the end of travel, where the stem hits the housing. The force just before the wall is the "bottom-out force" quoted in specs.
Comparing two switches
Overlay them in the switch table. Two linears with the same bottom-out force can still feel different if one starts much higher; the flatter one feels more uniform, the steeper one more springy.