i am a newer,
who can explain the function glClear() with me?
thank you!!

The documentation explains pretty ok what it does…

The glClear function clears buffers to preset values.

void glClear(
GLbitfield mask
Bitwise OR operators of masks that indicate the buffers to be cleared. The four masks are as follows. Mask Buffer to be Cleared
GL_COLOR_BUFFER_BIT The buffers currently enabled for color writing.
GL_DEPTH_BUFFER_BIT The depth buffer.
GL_ACCUM_BUFFER_BIT The accumulation buffer.
GL_STENCIL_BUFFER_BIT The stencil buffer.

The glClear function sets the bitplane area of the window to values previously selected by glClearColor, glClearIndex, glClearDepth, glClearStencil, and glClearAccum. You can clear multiple color buffers simultaneously by selecting more than one buffer at a time using glDrawBuffer.

The pixel-ownership test, the scissor test, dithering, and the buffer writemasks affect the operation of glClear. The scissor box bounds the cleared region. The glClear function ignores the alpha function, blend function, logical operation, stenciling, texture mapping, and z-buffering.

The glClear function takes a single argument (mask) that is the bitwise OR of several values indicating which buffer is to be cleared.

The value to which each buffer is cleared depends on the setting of the clear value for that buffer.

If a buffer is not present, a glClear call directed at that buffer has no effect.

The following functions retrieve information related to glClear:

glGet with argument GL_ACCUM_CLEAR_VALUE

glGet with argument GL_DEPTH_CLEAR_VALUE

glGet with argument GL_INDEX_CLEAR_VALUE

glGet with argument GL_COLOR_CLEAR_VALUE

glGet with argument GL_STENCIL_CLEAR_VALUE

Error Codes
The following are the error codes generated and their conditions.

Error code Condition
GL_INVALID_VALUE Any bit other than the four defined bits was set in mask.
GL_INVALID_OPERATION glClear was called between a call to glBegin and the corresponding call to glEnd.