Linux / Unix vi / vim: Open and Switch Between Multiple Files

I am new to Linux sysadmin work. I am using vi / vim text editor to edit files located in /etc/ directory. I open files using vi /etc/resolv.conf/etc/hosts I can edit the /etc/resolv.conf file only. How do I switch between the two open files while using vim text editor under Linux / BSD / Apple OS X / Unix like operating systems?

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