I'm having a problem in using thumb drive in linux. What must I do and how to mount it.

searching for 'thumb drive' around here would be a good start. This has definitely been answered and discussed many times. Good luck!

TQ Vincent_Vega. I'm still new in linux's world. Hope you can help me.

Well, before you plug it in, open a terminal and type the following:
tail -s 3 -f /var/log/messages (some stuff will show up but ignore it)
Then plug it in. About six or seven lines should pop up in that window; look for a line that has 'sda1' or maybe 'sda2' or even maybe 'sdb1'.....
If you find that line, you're set. Press Ctrl-C to stop the 'tail'. Decide where you're going to mount this thumbdrive (maybe use mkdir /mnt/thumb). Then type the command:
mount /dev/sdxx /mnt/thumb (you'll need to be root for this)
the 'xx' should be replaced to match what tail showed you. The /mnt/thumb is the directory that the data on the thumbdrive will show up in. If all goes well you can open /mnt/thumb and see it all.
If tail didn't show anything when you plugged in your drive let me know. We'll take it from there.

I faithfully followed your suggestion

tail -s 3 -f /var/log/messages

After I plug in the thumb drive, I get the following message:

Kernel: hub.c: USB new device connect on bus1/1, assigned device number 3
/etc/hotplug/usb.agent: Setup usb-storage for USB product 90a/1001/100

As you can see, I couldn't find any sda1 or sda2 at the message output. What should I do? Thanks!!!