To 'get' something means to either receive it physically such as a notebook. "I am (I'm) going to get a notebook." It can also mean to understand something. To register it in your mind. "I get this problem now." As for "I am (I'm) going to get you a woman." and "I am (I'm) going to get you a notebook." means that you are going to receive and present an object, the noun (in this case the woman and the notebook) to the person you're speaking to.

"Get" is one of these nebulous words that you need to understand in context. "I'll get you a notebook" means I will go, find and bring back a notebook for you. The same applies to "I'll get you a woman" - it means you will go and find a suitable girlfriend for your friend.

'Get you a notebook' is not correct English. If you are in class and you don't have a notebook, your teacher might say 'Get a notebook' or even 'Get yourself a notebook'. This means that you should go and find a notebook - for example, you should go to a stationery shop, buy a notebook, and bring it to the next lesson. The word 'get' has many different meanings in English, but this example 'Get a notebook' is one of the most important meanings. It means 'obtain'. NB 'Get' in the sense of 'understand', as in 'I get you', is an idiomatic and colloquial use. It is much less important than the meaning above.