If you are going to use an iPad then you need online software, which will be open on December 4. You cannot install/download desktop TurboTax to an iPad. Desktop software can only be used on a full PC or Mac.
The Mobile App is just a portal to the online version. The Online version is suppose to open on December 4.
https://turbotax.intuit.com/personal-taxes/mobile/
Difference between Online and Mobile App
How to use the Mobile App
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-use-the-mobile-app/00/26828
What is the minimum system requirement on an iPAD to do premier version of 2019 tax?
For an iPad or mobile device you have to use the Online web version or the Mobile App which is a portal to the Online version
Online version system requirements
Then I don’t need to download anything?
how do I start on filing taxes?
Since you are on the iPad you can use either the mobile app, or you can use the online version while on a mobile browser. Both are using the same program.
You can find more information by visiting the Turbo Tax website here, https://turbotax.intuit.com/personal-taxes/mobile/