How to take screenshot with computer or laptop ?

Just open the page which you want to take screenshot and click key Fn + Prnt Scrn on your laptop or Ctrl + Prnt Scrn on your computer then open paint on startup menu then paste it using Ctrl + V then crop what you want then save. Now your screenshot is ready to use.

How to remove "unable to connect proxy server" error ?

Go to control panel then click on internet option then click on connection tab then click on setting then uncheck  use of proxy server. it will solve your problem surely.