TPS gives a foreign citizen the right to live and work in the US for a set period of time.
In plain English, that means that the thousands of Ukrainians who currently have TPS in the US will be eligible for an extension (probably for 18 or 24 months). Otherwise, their status will run out on Oct. 19. For Ukrainians currently in the US who do NOT have TPS, they will be able to apply to get the status. That's a big deal for the roughly 140,000 parolees who entered under the Uniting for Ukraine program, and whose residency rights will otherwise run out in 2024 or early 2025.
We don't yet know how long the new TPS will last. But usually, such extensions go on for 18 or 24 months or so.
While this is a great step, it is NOT a substitute for giving Ukrainians (and others in similar straits) permanent residency rights. Congress still needs to pass an adjustment act to do that. The extension will in time expire. Moreover, what Caesar giveth he can taketh way (or his successor can). So this isn't the end of this issue. But it's an improvement, and it also gives more time for Congress to (hopefully) act.