How to grab part of a window

Hi I’m new to the forum and this is my first post.

Can anybody explain to me how I can grab a part of an SDL2 window and save that to a texture so I can draw it back on the window later on?

Thanks is advance folks.

int height=(your height)
int width=(your width)

if ( SDL_CreateWindowAndRenderer( width,height, SDL_WINDOW_SHOWN,
&m_window, &m_renderer ) != 0 )

Not sure if this helps.