Tesla releases new firmware updates for its cars at least once a quarter (with major releases taking usually around a year to a year and a half to come out). There are times when bug fix releases seem to come every other week. Knowing whether or not you have the latest requires knowing what your car has (the smartphone app tells you, as does the center screen) and what the latest version is.
Note that there are two update tracks now — one for people without an active FSD license, and one for people with an active FSD license. The former gets newer updates, while the latter (active FSD license) is usually a few months behind. If your car has a version that is greater than the latest FSD version (example from summer 2024: software version 2024.20.x is rolling out to non-FSD-license owners and has FSD 12.3.6, while software version 2024.15.x is slowly rolling out to FSD license owners), because Tesla will not downgrade your software version, you will not get the latest version of FSD until that FSD version is added to a software version greater than what you already have. This is confusing and annoying, but that’s the way it is.
A handy way to determine what’s rolling out is with the TeslaFi Firmware Tracker. TeslaFi is one of those third party applications mentioned in this question, but you don’t have to be a paid TeslaFi member to see this data. There is a setting in your Tesla under the Software menu for Advanced or Standard updates. Advanced means you get new, generally available releases right away, while Standard puts you in a queue of unknown length before your car will notify you it’s ready. Note that downloading firmware updates requires being connected to WiFi, and the actual update usually takes anywhere from 20 to 60 minutes; the car is not driveable while updating.