How to create your own wifi network in mac without internet cable
Unfortunately you can't use your Macbook to extend your wireless network in this way. It seems to only be able to connect to an existing Wi-Fi network or create its own. It can't extend an existing Wi-Fi.

Three options are:

1) Purchase a Thunderbird to Ethernet adapter so you can connect the Macbook to the network over ethernet and then share the ethernet connection over wireless.

2) Connect your iPad to your Macbook by USB cable and then share the Wi-Fi connection over "iPhone USB".

3) Share the Wi-Fi connection on your Macbook over "Bluetooth PAN". This last one is probably the most attractive as it doesn't involve using a cable of some sort.