My watch just has the time and the red thunder bolt sign wht does tht mean

Hello,

This is taken from Apple's website:

When your battery charge drops to 10 percent, your Apple Watch alerts you and asks if you want to use Power Reserve. When the battery gets too low, your watch automatically enters Power Reserve, and appears next to the time. Learn how to maximize your battery life and lifespan.

To turn on Power Reserve:

1. Swipe up on the watch face to open Control Center.
2. Tap the battery percentage, then tap Power Reserve > Proceed.

Turn off Power Reserve

To turn off Power Reserve:

1. Press and hold the side button until you see the Apple logo.
2. Wait for your Apple Watch to restart. You might need to charge your Apple Watch first.

More info here:

Check your battery and charge your Apple Watch - Apple Support

Okay try these steps:

If your Apple Watch won't charge or you see a message on your watch that charging with this accessory isn't supported:

1. Make sure that you plug the Apple Magnetic Charging Cable all the way into the USB Power Adapter, then make sure that you plug the adapter all the way into a power outlet.
2. Make sure that you're using the Apple Magnetic Charging Cable and the USB Power Adapter that came with your Apple Watch.
3. Completely remove any plastic wrap from both sides of the charger.
   
4. Make sure that the back of your Apple Watch and the magnetic charger are clean.
5. Position the back of your Apple Watch on the charger. The charger's magnets align your Apple Watch, and you should see on the watch face.
6. If your Apple Watch still won't charge, force it to restart. Press and hold both the side button and Digital Crown for at least 10 seconds, or until you see the Apple logo.
7. Try a different Apple Watch Magnetic Charging Cable and a different USB Power Adapter. If your Apple Watch is out of power, you might need to wait a few minutes for to appear after you start charging your device.
8. If you still need help, contact Apple Support.

More info here:

If your Apple Watch won't charge or it won't turn on - Apple Support

that happened to my watch and I left it to charge while I went to work. I come home, and it's the same. It didn't seem to charge, and everything is plugged in correctly. Please assist

It may not have made contact correctly. After you place the watch on the charger it should make a sound to indicate it is connected properly.