When my car shifts into 2nd gear (automatic transaxle) it gives the car a big jerk.Is this serious?

Here's what I would do:

. Drop and clean the transmission pan, change the filter, and refill with Mobil 1 Synthetic ATF. Repeat this process every 30,000 miles.

. Disconnect the negative battery cable overnight, to force the PCM to relearn shift points.

https://www.askmehelpdesk.com/cars-trucks/when-asking-about-your-vehicle-303903.html

Check for vacuum leaks to the transmission's modulator valve, if equipped.
You may have a worn/broken motor mount(s) as well.