To get any app other than the basic ones Apple provides with any device, you need to sign into the App Store. To do this you must have an Apple Account (such as the one you used to sign into this forum to be able to post here). Go to the App Store app and sign into your account. If you have downloaded this app previously it should show up under your purchases. If not, search for the app and tap "Get".
Read this document to learn how to download apps and games on your iPhone or iPad
Download apps and games on your iPhone or iPad - Apple Support
If you do not see the app in your purchase history it may have been purchased by a previous owner of the device or another person who signed into your device. That app is tied to their Apple Account and can only be re-downloaded by them. You can download it but you will have to buy it again. For that you will have to add a payment method.
By the way, some of the top helpers on this web site are also "seniors" so age does not necessarily mean an inability to work with computers. I saw a show yesterday where a 104 year old Japanese man spent his time programming apps. ;-)