Adding filter code to a new Applet
To add filter code to a new Applet, head to https://ifttt.com/create and select a trigger and add at least one action. Now, click the first plus button ( + ) and click Add filter. You can use the generators on the right, or write your own code.
When you're finished, click Create filter > Continue > Finish, and you should be all set!
For information about adding filter code in the IFTTT mobile app, check out the article Can I add/edit filter code in the IFTTT mobile apps?
Adding filter code to an existing Applet
To add filter code to an existing Applet, head to https://ifttt.com/home, select your Applet, and click Settings. Now click the first plus button ( + ) and select Add filter.
When you're done, click Create filter, then Update, and you should be good to go!
Available methods for your Applet's trigger, queries, and actions
All available filter code methods for your Applet's trigger, queries, actions, a couple of methods available to all Applets (Meta.currentUserTime and Meta.triggerTime), and filter code generators will be displayed on the right:
Learn more about filter code and the possibilities it unlocks here. Even if you're not too confident writing code use the built in filter code generators to get started!