Sorry, I am a bit confused when you use the term "Hotspot".
If the AirPort Extreme is broadcasting a wireless network now, you already have a "Hotspot".
If your wireless network is password protected, then clients will need to be given the password so that they can connect.
Or, are you perhaps saying that the AirPort Extreme has not yet been configured to provide a wireless network?
Open Macintosh HD > Applicatons > Utilities > KeyChain Access
Locate the line with the name of your wireless network and AirPort Network Password
Double click this line
Enter a check mark next to Show Password
Enter your main administrator password for your Mac
Your wireless network password will now be revealed
The ability to setup a separate Guest Network will depend on two factors:
1) You have a newer dual band AirPort Extreme. Any new product purchased in the last 2-3 years would qualify in that regard
2) You have a simple modem connected to the AirPort Extreme, not a combination modem/router or gateway type of device that most service providers furnish to their customers.
To check and see if you will be able to utilize the Guest Network feature on your AirPort Extreme.....
Open Macintosh HD > Applications > Utilities > AIrPort Utility
Click on the AirPort Extreme icon and then click Edit in the next box that appears to the right of the AirPort Extreme
Click the Wireless tab at the top of the next window
Look for a box that will allow you to enter a check mark next to Enable Guest Network
Enter a Name for the network
Enter a Guest Network Password for the network and Verify the password
Click Update to save the new settings and allow 30 seconds for the AirPort Extreme to restart
If you do not see an option to Enable Guest Network, you might want to check with your service provider to see if they can supply you with a simple modem.