Install input method
Browse Input method
You can browse input method supported by Fcitx with Category:Input_Method.
You'd better install it with your distribution package management software, usually the input method is in the same repo from which you install Fcitx. All Fcitx related package is start with fcitx, so you will see it when you search fcitx.
After you install
First you need to restart Fcitx, you can simply exit with menu and run fcitx again, or you can use
Some input method will be added to the list by default (Usually for the package with only one input method inside), some will not. You might want to add those into list with configuration tool, and adjust some option to meet your needs.