why cant i use my wifi for notebook

Please make sure if your wi-fi driver is installed properly. Which NetBook are you using?
Type this " lspci " in Terminal and press Enter (without the quotes). Copy and paste the data over here.

jason@jason-Compaq-Presario-CQ50-Notebook-PC:~$ lspci
00:00.0 RAM memory: nVidia Corporation MCP78S [GeForce 8200] Memory Controller (rev a2)
00:01.0 ISA bridge: nVidia Corporation Device 075e (rev a2)
00:01.1 SMBus: nVidia Corporation MCP78S [GeForce 8200] SMBus (rev a1)
00:01.3 Co-processor: nVidia Corporation MCP78S [GeForce 8200] Co-Processor (rev a2)
00:01.4 RAM memory: nVidia Corporation MCP78S [GeForce 8200] Memory Controller (rev a1)
00:02.0 USB Controller: nVidia Corporation MCP78S [GeForce 8200] OHCI USB 1.1 Controller (rev a1)
00:02.1 USB Controller: nVidia Corporation MCP78S [GeForce 8200] EHCI USB 2.0 Controller (rev a1)
00:04.0 USB Controller: nVidia Corporation MCP78S [GeForce 8200] OHCI USB 1.1 Controller (rev a1)
00:04.1 USB Controller: nVidia Corporation MCP78S [GeForce 8200] EHCI USB 2.0 Controller (rev a1)
00:06.0 IDE interface: nVidia Corporation MCP78S [GeForce 8200] IDE (rev a1)
00:07.0 Audio device: nVidia Corporation MCP72XE/MCP72P/MCP78U/MCP78S High Definition Audio (rev a1)
00:08.0 PCI bridge: nVidia Corporation MCP78S [GeForce 8200] PCI Bridge (rev a1)
00:09.0 IDE interface: nVidia Corporation MCP78S [GeForce 8200] SATA Controller (non-AHCI mode) (rev a2)
00:0a.0 Ethernet controller: nVidia Corporation MCP77 Ethernet (rev a2)
00:0b.0 PCI bridge: nVidia Corporation MCP78S [GeForce 8200] PCI Express Bridge (rev a1)
00:14.0 PCI bridge: nVidia Corporation MCP78S [GeForce 8200] PCI Bridge (rev a1)
00:18.0 Host bridge: Advanced Micro Devices [AMD] Family 11h Processor HyperTransport Configuration (rev 40)
00:18.1 Host bridge: Advanced Micro Devices [AMD] Family 11h Processor Address Map
00:18.2 Host bridge: Advanced Micro Devices [AMD] Family 11h Processor DRAM Controller
00:18.3 Host bridge: Advanced Micro Devices [AMD] Family 11h Processor Miscellaneous Control
00:18.4 Host bridge: Advanced Micro Devices [AMD] Family 11h Processor Link Control
02:00.0 VGA compatible controller: nVidia Corporation C77 [GeForce 8200M G] (rev a2)
07:00.0 Ethernet controller: Atheros Communications Inc. AR5001 Wireless Network Adapter (rev 01)
jason@jason-Compaq-Presario-CQ50-Notebook-PC:~$

See here for instructions on how to install the driver.

http://ubuntuforums.org/showthread.php?t=1309072

Also you could try enabling the backports repository.

i've always have this problem when im installing ubuntu, it just don't detect the wifi connection so i always need to use internet via cable to install the updates while running the installer, my notebook is a dell inspiron 1525, could you guys fix it please?

 :)