I'm so damn confused?

Straight talk is pretty straight forward $45/month for unlimited talk text and data and tethering is restricted. They usually have really good data on their phones. 

Wifi is usually Much cheaper than a data plan. Unless they only go online to check email once a week.

Just buy a package of a suitable size if the person cannot use their home wifi.  If they are going to download massive new games then plenty.

Example: https://www.whistleout.com.au/Broadband/Guides/how...

restart the qhole system 

WiFi is free to use but will only save you money if the phone can connect to it. If not, the phone falls back to cellular data and the meter starts running. Even then, if your friend is not a heavy user (e.g. no video) the low end data plan might be enough.

However, tread very carefully if a laptop is involved. Every bit that computer gets via the phone will cost money.

Wifi doesn't cost anything to use (except a tiny bit for power). 

What Does cost is data handling.  

There is no point in paying for a data plan that won't be used. 

I don't understand what's so damn confusing. Wi-Fi is simply a wireless method of communication between a device (like a phone or PC) and a Wi-Fi router. That's it. You don't pay for Wi-Fi in most typical home network situations. You pay for Internet access from the Internet provider, which in turn you can use Wi-Fi to access the Internet through the router. Mobile data on the other hand, is the mobile Internet connection between the phone and the carrier's cell tower.

If the person is only using Wi-Fi, then it makes no sense to pay for a data plan. However, I'm not sure what carrier you have but as far as I'm aware, most major carriers will require a mobile data plan if you're using a smart phone.

Just one more thing I'm not sure based on your question. You say that the person in question can't use Internet at home. So does that mean that he/she cannot use Wi-Fi at home or what?

If the person will be "using only Wifi" then how would getting a plan that is priced for using data more than wifi be helpful to them?  They are not going to use it.

Also keep in mind that if they will be using this phone at their home most of the time, and they have wifi for their computer, tablet, iPod, etc., they can hook their phone to that wifi and nnot have to use either their phone wifi or their phone data.  They can use their home wifi for free.  (As long as they are within range of it.)

Wifi. The user is already paying for internet which is what is behind the wifi so they aren't going to pay a second time to give their phone internet access. That is cheaper.

This other person doesn't have wifi so they have to use the phone's data which is going to consume their phone's data plan.

Opt for the free Wifi.

How is it confusing lol