I need to configure wireless network. To do it I need to install CA certificate. How to do it in ubuntu?
Some wireless networks use a Certificate Authority file which can be configured in the following place:
Network menu (the four spreading arcs icon) > Edit Connections... > choose your network > Network Security tab > pick "WPA & WPA2 Enterprise" from the pop-down menu > CA Certificate.
(My own use for a CA file is a VPN that requires me to install a CA in my browser. That doesn't seem to be your case.)