If you are reading Info in Emacs, you can select a new independent
Info buffer in a new Emacs window by typing M-n. The new buffer
starts out as an exact copy of the old one, but you will be able to
move independently between nodes in the two buffers. (In Info mode,
M-n runs the Emacs command clone-buffer.)
In Emacs Info, you can also produce new Info buffers by giving a numeric prefix argument to the m and g commands. C-u m and C-u g go to a new node in exactly the same way that m and g do, but they do so in a new Info buffer which they select in another window.
Another way to produce new Info buffers in Emacs is to use a numeric
prefix argument for the C-h i command (info) which
switches to the Info buffer with that number. Thus, C-u 2 C-h i
switches to the buffer *info*<2>, creating it if necessary.
If you have created many Info buffers in Emacs, you might find it difficult to remember which buffer is showing which manual. You can use the command M-x info-display-manual to show an Info manual by name, reusing an existing buffer if there is one. When given a prefix argument, this command limits the completion alternatives to currently visited info files, thus giving a convenient way to switch between several manuals.