Lets do some information collecting then do some testing.
Click on the Apple (top left)
About this Mac
Now look for Network and WiFi
There you will see the information about your WiFi card and the status of the connections.
It looks like this:
As next step I suggest to do some Diagnostics.
Than open the Network Diagnostics to test your WiFi connection.
Choose Apple menu > System Preferences, and then click Network.
Click “Assist me,” click Diagnostics, and then follow the onscreen
This test will tell you about your WiFi card and connections.