IFTTT's pricing plans have changed a few times over the years. Most notably even having a paid plan at all hasn't been the case for much of IFTTT's existance. Starting with the Free plan this will give an overview of what's included and what the restrictions are.

Price

Since this is the lowest tier free plan you can probably guess the cost is in fact free. Literally zero dollars for as long as they have this service available.

Applets

Applets are the automation workflows that you can set up or copy from their community. For the free plan you are limited to 5 Applets being active at any one time in your account.

Speed

Speed is something that can often be overlooked and importance will depend on what your objective is with any automation. Instant or realtime speeds in any online automation service is not something you should expect to happen no matter how much you end up paying, everything is a trade off. For the free plan you are considered to get standard Applet speeds. In practice this depends on the types of triggers and for something that needs to poll or check every so often you can expect up to an average of 1 hour but often less.

Features

For features you get all the basic features you'd expect that IFTTT offers. This means building trigger and action automations, access to their community Applets, use of the mobile app (which is a convenient way to tie your device to automation) and also how many times Applets can be run. In the case of IFTTT you can run your maximum of 5 Applets an unlimited number of times, even on the free plan. This isn't something you will find with other automation services.