I just realized that when my WIFI gives access to my network that guests of mine will be able to access my disk server and my computer. I don't want this what can I do?
This should be a concern for business ans well as even home WIFI. If you let people use your WIFI, make sure it is protected. You should protect information on your network. Especially if you let people use your WIFI.
Most newer WIFI routers have the ability to support "guest" users. Guest users will have the ability to get access to your WIFI, but will not be allowed to do anything other than to go to the internet.
If you have network accessible data that guest user will not be able to see or access your local network devices.
Some people also remove a password to access their WIFI network. This is also a very bad decision. You may trust your friends, but if you have no password anybody can not only get to the internet using your bandwidth but then can get access to your devices on the network.
Another option is to not broadcast make your WIFI name (SSID). This way the cheap neighbor next door who knows the kids and dog's name that you use as a password to not even see that you have a WIFI.
Protect yourself and your network. Use a hidden SSID, have strong passwords, and use guest networks.