Lintel level and sill levels are parts of the wall.
When a window or door is constructed, a load of bricks above it needs a base. And lintels are provided for the same. Above the window, a beam-like structure mostly made up of concrete (Structural wall) is constructed. the length of this beam can limit to slightly more than the length of the window or it can exceed to cover the whole wall and can act as a lintel beam. the height where the lintel beam is constructed is called lintel level
The sill level are similar to the lintel level but it is constructed below the window and its length is the same as the length of the window only. the height at which this sill is constructed is called the sill level.