Very slow

Slowness/high CPU usage could be due to (but not limited to):
– A poor or memory intensive theme. Switch to the WordPress default theme (Twenty Sixteen, etc.) and test loading time and see if you see a difference. If you do, may be your theme can be re-written to be more efficient.
– Poor or memory intensive plugins. One by one disable plugins and test loading time and see if you see a difference. If you do, may be that plugin can be re-written to be more efficient.
– your server is slow (e.g., “process hang”, overload, you get a lot of visitors, other problems, etc.); generally, every inexpensive host out there is slow.
– lots of images.

Test your site at (free online testing):
https://gtmetrix.com/leverage-browser-caching.html OR https://www.webpagetest.org/
https://tools.pingdom.com
https://developers.google.com/speed/pagespeed/insights/

Also, review these resources:
– https://www.wptavern.com/determining-which-plugins-are-slowing-your-site-down
– https://wordpress.stackexchange.com/questions/656/is-there-a-way-to-measure-server-resource-cpu-usage-by-wp-plugins/
– https://www.ads-software.com/plugins/plugins-speed-test/
– try installing the Query Monitor plugin and seeing how long the queries are taking.
– https://www.wptavern.com/my-performance-woes
– https://codex.www.ads-software.com/WordPress_Optimization
– https://codex.www.ads-software.com/High_Traffic_Tips_For_WordPress
– https://codex.www.ads-software.com/WordPress_Optimization/Caching
– https://codex.www.ads-software.com/WordPress_Optimization/WordPress_Performance

sir, I have no problem when i open my website in browser. But problem seen when i working on it. Even I can not creating pages.

I want to make sure I understand. Are saying the slowness affects the admin area only?

yes, when i creating pages, managing themes, menus, plugins.

Have you tried:
– Flushing any caching plugins you might be running, as well as server and/or browser caches. Also, any op cache or content network cache, as well as Cloudflare, clear those caches.
– deactivating ALL (yes all) plugins temporarily to see if this resolves the problem (plugin functions can interfere). If this works, re-activate them individually (one-by-one) to find the problematic plugin(s).
– switching to the unedited default Theme (Twenty Sixteen, etc.) for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins).

I flushed caches, deactivated all plugins cleared browser caches, cookies. I have latest firefox. But still same

This happens
https://i68.tinypic.com/4f3iv.jpg

same problem pls help anyone

Try reviewing this:
https://wordpress.stackexchange.com/questions/166727/how-can-i-speed-up-my-wp-admin-section